Having owned a vast assortment of DAPs including Zune HD, iPod Touch 4G, Archos 604, 605, 5 IT, iRiver Clix, etc. This is definitely the best sounding DAP I have ever owned. The built in amp works extremely well with my UE11Pros to give crisp clean bass which is still quite strong straight out of the headphone jack. Mids and highs are clean and natural without any shrillness at high volume. I rarely go past the half way point on volume, the AMP is quite strong even without an additional amp.
Downside for me is the lack of FLAC support. However, I have learned the trick of using MediaMonkey to convert FLAC to WAV and that loads successfully to the Walkman in a lossless format.
The user interface is pretty good, although Zune and iPhone are better. The best thing about the user interface is that you can bring the display back up just by tapping on it, then the play button is easily accessible. There are dedicated buttons for play and volume control which I love -- something that is missing from most other touch screen DAPs.
The OLED display is bright, colorful, and crisp. Displays the album art very nicely.
Build construction is excellent, this is a solid unit that has some heft to it.
For pure sound quality, I would highly recommend the Walkman X even though the price is a bit on the high side -- you get what you pay for.