I did tons and tons of research before settling on this. I knew exactly what I was looking for and the D2 met my requirements almost to the letter. So maybe I can save you some time and effort if you share my tastes. My requirements, which the D2 satisfies:
- 16 GB flash memory. More importantly, expandable via SD / SDHC cards. This means this thing is going to last me a good long time. 8GB of flash memory is $20 or less nowadays, and there are already 32GB cards though they're crazy expensive. The price is going to drop fast though, giving me almost unlimited storage space.
- Shows up as a simple FAT partition. This is essential for me. (Also supports MTP, if you can stomach it.) Music transfer via Devices in Amarok 1.4 works just fine.
- Folder browsing or ID3 tag browsing. I obsessively tag my music, so I like that way.
- Supports non-Latin alphabet filenames and tags. Most of my music is Japanese, so this is also essential for me. Cowon is a Korean company anyways, so they've got this down. The interface itself can be switched to many different languages, which is nice.
- Audio codec support: MP3, FLAC, OGG, WAV, WMA, APE. You can't beat that. All I needed was MP3, OGG and FLAC, but the others are a nice bonus.
- 52 hours of battery life for music, optimally. You'll never hit this in real life, but you're still likely to get almost two days worth of playtime. Comes with an A/C adapter, charges in 3.5 hours. Can also be charged via USB, of course. (The USB connector is a standard cable, no proprietary garbage, which is also nice.)
- Displays album art, including embedded art in MP3 tags.
- FM radio.
The only one of my requirements the D2 didn't meet was to have a replaceable battery. From what I've read of people who disassembled this thing, the battery is screwy and may be difficult to replace, but I'm not too worried.
The D2 does lots of other things I don't care about, like playing movies and displaying pictures and text files and Flash, and it has a scientific calculator and displays the time and so on. All I wanted this for was to play music, and it does that amazingly well.
The sound quality on the D2 is noticeably better than my old Muvo. It sounds very good. There are a lot of equalizer settings, bass boost, and a bunch of things I don't understand. I turned them all on, and everything sounds awesome. I can turn this thing up VERY loud (ear-shatteringly loud) before getting any distortion. With my Grado SR80's, music on the D2 sounds as good as or better than the sound card in my computer.
The touch-screen interface is good enough for me. I'm not thrilled by such things and I'm smart enough to adapt to any usable interface; "user-friendliness" was not on my list of priorities. I'd rather have power than simplicity, and this gives me the power I want.
This player is like the KDE of MP3 players; there are options for almost everything you can think of. The interface is crammed full of information but the stylus works well to get through it. If you like a dumbed-down minimalist iPod click-wheel kind of interface, the D2 isn't for you. The D2 also has three hardware buttons, two for volume and one for menu, and their function can be customized.
All of this for $175 from amazon.com. This is a very good time to buy a D2, because the next generation of Cowon players is right around the corner. The D2 is likely to be discontinued in favor of fancier, flashier, more expensive but less awesome players. I couldn't let this pass.
AnythingButIpod has a good review of this player including videos.