Recently I forced myself to uninstall Amarok 1.4 and try Amarok 2 again. I saw there were some nice updates to the interface coming in the next version so I grabbed the latest version from SVN.
I very quickly started looking for other alternatives, and you'll soon see why. The best I could find was Songbird.
I'll start with a disclaimer that both of these programs are great, and they are free. I am not suggesting, let alone demanding, that anyone change anything in either program to suit me. Kudos and thanks to the devs of both. These two programs are both probably better apps than I could dream of coding. Feel free to respond "Ask for a refund" and "Fix it yourself" anyways if you like. I think it's still useful to give some constructive feedback, and maybe I'll learn something myself about how to make a good GUI along the way.
Next I'll start with my conclusion, so you don't have to read further, because this is admittedly long. Amarok 2's interface is extremely painful, but at least it plays music. Songbird has a wonderful interface, much like Amarok 1.4 had a wonderful interface; if only I could get Songbird to make sound come out of my speakers, I'd be set.
I think it's interesting to compare Songbird and Amarok 2, both being bleeding-edge music players for Linux with a similar philosophy and feature set. So let's compare GUIs. I sized the two windows exactly the same and tried to have them display mostly the same bits of information, so it'd be easy to compare. Click below for larger versions.
Amarok 2:

Songbird:

Playlist
In Songbird the playlist dominates the window by default. This is good because seeing a list of music is what I want. It's the whole point of a music player.
I strongly dislike the "filter pane" style of browsing my music. Thankfully you can turn it off in Songbird. You can also install "cover flow" sorts of eye-candy extensions if that floats your boat. I avoid such things, and Songbird's interface is easy and comfortable by default.
In Amarok by default the playlist is a little sliver of GUI off on the right, and the middle context pane dominates the window. Enough people complained about this that in later versions you can turn off the context view entirely, in which case the playlist will stretch to a reasonable size. Whether the information in it will look good is another story (see below).
Amarok's "Local Collection" browser is an expandable tree. You can customize how things are grouped. This was great in Amarok 1.4. It works similarly here. It's not as lightweight or responsive as in 1.4, but I can't complain. By default it's way on the left, with the playlist way on the right and the context view in between, but in later version of Amarok you can change the order of the panes.
I'll call this a tie even though you have to fight for it in Amarok.
Sorting the playlist
Songbird has a bunch of columns with column headers. To sort things you click the headers. Note that this is how Amarok 1.4 worked. This is how every program in the universe works.
In Amarok you have drop-down menus that you can add and remove with buttons, and you pick sorting criteria from that list, left-to-right in order of priority. This is clumsy. According to the devs' blogs this part of the GUI is a work in progress, which is fine, maybe it'll improve.
But note that the design of Amarok's playlist fundamentally limits the ways you can sort it. There have to be some magic GUI controls floating up top, disconnected from the playlist. You aren't going to get a bunch of column headers that you can click because the playlist isn't just rows and columns. Each song in the playlist can take up more than one row and there are grouping-headers interspersed. This is painful and I imagine it's always going to be painful.
Playlist readability
There are no labels in the Amarok playlist to tell you what information you're looking at in the playlist. I initially customized my playlist to show disc number and track number. Doing so, you get a bunch of numbers. What do the numbers mean? At a glance you can't tell. Am I looking at an Artist or Composer? Play Count, or Score? Does that big empty space mean my song is missing a Genre or missing a Year?
In Songbird the columns have headers.
Playlist length
How many songs can you squeeze into the playlist vertically? This is an important metric for me. I want to be able to find a song quickly without scrolling through a list for a year and a half. Sure I can search, but search doesn't replace my eyes in all circumstances.
In Songbird even with those filter panes above the playlist it fits a few more songs than Amarok. You can turn off the filter panes entirely, in which case you can display tons more songs in Songbird than in Amarok. Songbird wins.
In Amarok, by default the playlist has a bunch of multi-row header stuff mixed into the middle of your playlist to show artists and album names and cover art. You can make the headers not take up so much room (or turn them off entirely), in which case Amarok gets pretty close to Songbird. You'll just do without album or artist names. Unless you can manage to cram them into the playlist in the rows beside the track titles.
Which brings us to our major problem...
Playlist customizability
In Songbird you can right click and add and remove columns. You can drag-and-drop columns to rearrange them. You can drag the edges of the columns to resize them. It's simple and it works. This is how Amarok 1.4 worked too.
Amarok fails hard in comparison. In Amarok to customize the playlist you go into a special dialog. You pick your components from a horizontally-scrolling list of huge icons. Then you arrange them into rows.
You can put two or more items side-by-side in which case they become multiple columns on that row in the playlist. Kind of. To control the width of the columns, you hover over that component in this magical dialog, and a weird circular icon appears. When you click it, a drop-down appears with a microscopic slider at the bottom that looks like it was pulled from KDE2. This is the only way to resize columns in the playlist. Here's a screenshot.

What in the world is this? What are simple drag-and-drop operations in Songbird and every other application ever made, are buried in this cryptic dialog under non-standard controls in Amarok. I've been using KDE and Amarok for a long time and it took me a good couple minutes to even figure out how this thing works.
I think the widths are percentages and have to add up to 100%, I don't even know. The slider is so small that if you drag it one pixel it usually jumps 5-10%, so it's nearly impossible to get anything to look nice. And when you resize the Amaork window later, the columns don't resize sanely; some fields are smashed into each other or overlap as others take up too much space.
Maybe this will all be fixed before the next release; I realize I'm looking at bleeding-edge pre-release software. But this whole idea is so fundamentally broken I don't know how it's going to be salvaged.
I've heard many times that "You can make Amarok 2 look like Amarok 1". No you can't. You can tediously stuff lots of information into the playlist so that it approaches the level of info you could easily and painlessly get in Amarok 1.4. But it will neither look nor act anything like Amarok 1.4. Resizing the playlist will break things. Nothing is labeled. Nothing is easily customizable.
Playlist consistency
Songs in Amarok are grouped into albums by default. If you have a song that doesn't belong to any album, it's displayed completely differently than a song that does. You can alter this in the scary playlist editor dialog mentioned above, under the "Single" tab (as opposed to "Head" and "Body" which control the "grouped" songs). Sound confusing? It is. Needlessly so.
In Songbird songs are displayed the same whether they belong to an album or not, since the play list is just a list of songs. This seems like it should be a no-brainer.
Playlist: overall
Amarok 2's playlist is unique, imaginative, and I'm sure it's a clever bit of code. It's also nearly unusable.
Why can't we have a grid of rows and columns? There's a good reason so many apps use such a control. It's simple and familiar and it works. I'm open to learning something new if it's an improvement. Amarok 2's playlist is not an improvement. Why can't the playlist be a simple list of things to play?
There's nothing about QT4 preventing someone from making a good GUI. Look at ktorrent.
The little things
Say I want to email or IM someone and ask them if they like some artist, whose name happens to be Japanese and difficult to type on my gaijin keyboard. How do you copy and paste the name of an album or artist in Amarok 2? In Amarok 1 you could just click any field in the playlist twice, and it'd let you edit or copy/paste that field inline. Same in Songbird.
In Amarok 2, you have to right click and go into the Edit Song Details dialog, and do it from there, then close the dialog. A tiny step backwards.
How do you change the rating of a song? In Songbird you click the stars in the playlist beside the song you care about. Same in Amarok 1.4.
In Amarok 2, you can display the stars for each song in the playlist, but to change the rating you have to click in the context pane. (So if you dislike and therefore hide the context pane, you're screwed.) Clicking in the playlist does nothing. A tiny step backwards.
All of these tiny steps add up.
Extras
So how well does each player serve as a web browser?
This seems like a ridiculous question, except that both really do try to be a web browser. You can open song lyrics and wikipedia pages and such things right in the music player. I find these features nearly useless. Lyrics are nice when it works (which isn't often, for the music I listen to), but browsing Flickr? Really? Does someone really use this?
Songbird does use its inline browser in a nice way to let you browse and install addons from the Songbird website, and Songbird has a cool feature to let you rip audio files from web pages. Amarok doesn't have these, but I don't hold that against it. I can easily live without any of this stuff.
So in Songbird you have an embedded Mozilla engine. It's hidden behind a tab. You can just avoid opening such a tab and then you don't see it. You can even hide the tab bar itself. Victory.
In Amarok the browser stuff inhabits the middle context pain. The size is limited for this pane, which means information is crammed into the available space, which greatly limits its use. It's also clumsy and difficult to turn components on and off, and I can't figure out how to resize them. The context view itself is either in your face, taking up most of your screen real estate, or it's gone and not easily retrievable.
Note in the screenshot, how in Songbird the lyrics pane is big enough to display all the lyrics, yet small enough not to be annoying. You can also hide the pane (as you can hide every other pane in the GUI) via that tiny button with an arrow under the pane. Amarok's lyrics widget is either too big (if you let it occupy the whole content pane) or too small (if you want to have anything else in the pane with it).
Note that Songbird's lyrics pane is added via an addon. It's a completely optional part of the GUI, which is nice. (Note that Songbird also mangles certain text in the lyrics due to encoding problems, which is a point against it.)
Wasted screen real estate
See that tiny little red icon in the bottom-right of Songbird? That's the Last.fm integration. It's all hidden in a little square of pixels, out of my face, not sucking up screen real estate. This is a common theme in Songbird. Everything is tiny and/or hideable. Tiny is good.
In Amarok everything is huge and round. Even ignoring the content pane, there's white space everywhere. There are buttons strewn all over the interface, like the seven in the lower right. Export Playlist? Does that really need a button? And other buttons appear (and disappear) in awkward positions at the top. "Add Position Marker"? Does this really deserve a prominent button right beside the main play controls?
And yet things I do need buttons for, such as changing the Skip or Repeat options, have no buttons. This is possibly the first player I've ever used that doesn't have a button for Skip and Repeat.
GUI skinning
Songbird is skinnable. So was Amarok 1.4, to a degree. Amarok 2 isn't and I don't know if it ever plans to be. I can live without skins but it's nice to have the option.
Desktop environment integration
As one might imagine, Amarok wins here, if you use KDE, as I do. Global keyboard shortcuts are already set up, it sits in the system tray, and there are nice Plasma applets you can put on your desktop.
Songbird meanwhile does not play nice. First, it has window hints set to hide its border and window title bar, and it tries (and fails) to manage windows itself, giving your window manager the middle finger. I had to force kwin to display the title bar and border just so I could resize certain dialogs that were otherwise broken.
Then, Songbird doesn't sit in the system tray. You can force it down there via alltray, but right-clicking the icon doesn't give you Play/Pause/Next/Back options like in Amarok.
There are no global hotkeys, but you can easily fix this in KDE too because you can set your own global hotkeys to do anything, and Songbird has a commandline interface to let you do what you need. It's still not as graceful as Amarok.
So KDE thankfully rescues Songbird from its own deficiencies, which is nice. Except...
Playing music
Ah, Songbird. Why oh why won't you work? Songbird uses gstreamer. In my years of bouncing between Gnome and KDE and XFCE and others, and using various distros, gstreamer has never worked for me consistently. I can get Songbird to play music, but Flash videos stop producing sound while Songbird is running. This is a known and reported bug, I'm not the only one. While Songbird is playing, other KDE apps randomly produce sound or not depending on the phase of the moon.
Amarok actually plays music, so I'm stuck with it. Unless I go back to Amarok 1.4 which I may still do.
Conclusion
Songbird is pretty good. If I can figure out how to make gstreamer play nice, I'll probably use it.
Otherwise just consider this yet another voice in the wilderness wishing for a Qt4 version of Amarok 1.4. There was nothing wrong with it, from a user's perspective. I'm not the first wishing for this, and won't be the last. If I had a couple years to get good at C++ and a team of programmers to help, I'd probably try it myself.
Why write an 87-page essay about the GUI of a music player? Because Amarok 1.4 was a really good program. I'm a programmer and I appreciate a good program. Songbird has a pretty darned good GUI too. It's painful to see Amarok 2 going in this direction.