Well, I just got my X02 yesterday. Pretty impressed overall, especially for the price.
The biggest takeaway is that the battery life is ridiculous. I've had it going since I got it, at 3PM yesterday, playing non-stop, and it's still got 30% battery life left. That works out to somewhere around 40 hours or more of total battery life. Even my Sansa Clip was lucky if it could get 15 hours and that was the 'battery king' of yesteryear.
Another thing to note is that it gets extremely, extremely loud. Instant ear damage loud. The volume bar goes up to 30 and I found most headphones and IEMs to be ear-splittingly painful after 15. Normal listening volume is around 6-10. PLEASE, PLEASE check the volume and make sure it's below 15 BEFORE PLUGGING ANYTHING IN. I'm serious.
The overall sound quality is quite good. There is some lack of spaciousness, and some roll off on the extreme ends of the spectrum. No hiss at all with the few headphones, IEMs, and speakers I've used. Detail is good but you can tell there's some missing microdetail when compared to a more refined source... not really surprising at all. Definitely not what I'd call "poor" sound. Great for the price.
The X02 actually feels great, really solid with a nice textured silicone skin. The buttons click nicely and everything has nice tolerances and works, mechanically, great.
Now, for the less than great parts: the screen quality approaches terrible. Very low resolution and the font for the player is large and unchangeable (as far as I can tell). You can only read one or two words of a song at a time. Really cramped and hard to navigate through.
Also, no ID3 support that I can see. Which also means, no proper sorting -- yet there are sections to view by artist, album, etc., but they don't work reliably for me. Perhaps it uses a tagging system I'm not familiar with? It also doesn't list tracks in order, like it will go 03, 11, 04, 01, 08, etc.
And the navigation choices for the buttons are very strange. It must be a cultural thing because I've seen it before on other Chinese players, but it makes little sense to me. Up does nothing most of the time. Down backs out of a screen (usually). Left and Right are what actually cycle up and down through a list -- unless you're on the main screen (of course! lol...) then all four directions work as one would imagine. Very quirky, but at least all the buttons respond well.
A super purchase for the money. I wanted a "disposable" MP3 player with super long battery life so that I can keep it in the car. That's exactly what I got. The battery life on the X02 is otherworldly. I also think it wouldn't have any problem powering 300 ohm or maybe even 600 ohm headphones, due to the ridiculous volume capability, though of course the quality and battery life will suffer compared to a more expensive solution.