Pros: Audio quality, size, ease of use (Rockboxed).
Cons: Small text, build quality, mediocre battery.
I got this as a present for Christmas and so far I've been very impressed with it. Initially, my laptop had problems interacting with it as there wasn't obviously any driver but after having installed Rockbox it works fine and I'm able to drag and drop files from my computer onto the device with ease.
The reason for wanting the device is because the two HTC mobiles I own both have poor poor sound quality; bloated bass and hissing/pops/squeaks during quiet parts of the track just make for an unpleasant listening experience. I was pretty much sold by the flat frequency response and high sq to price ratio and I feel it's more than delivered. I've found that it's easy to find my way around despite the small screen and thus small text and the size means it's very pocket friendly.
On the down side though, I found the buttons feel quite cheap and there isn't much weight to the device which leaves it feeling a little lacking in terms of build quality and another gripe is that it won't drive my 80 ohm Beyerdynamic DT770 pros to I loud enough level without distortion though this is to be expected of a mobile device I guess..
Overall, I think it's a great little device and well worth the money I paid for it!