Well, I'm using this with an Audio Technica ES10, to give a point of reference.
To my ears, this is a very, very nice match, and really brings out the best in the ES10, as far as using it unamped goes. Coming from the Zune, which I always felt was no slouch regarding SQ without EQ, I can tell things are overall better. Bass is deeper and tighter at the same time and this player (maybe it's the S-Master MX amp) is really on the punchy side, without the music giving the impression of being compressed. I also use no EQ with the Sony, everything is as direct as possible, meaning no Clear Bass, no DPC, nothing but the direct signal.
The depth is also superior to the Zune, with, I feel, better separation and presenting a more detailed sound without being, to my ears, analytic. Soundstage is also perceptively improved over the Zune. I know some in this thread before have said that they feel the player is on the cool side, but that's not my impression. The highs are nicely defined, no sibilance in view or any harshness. That said, the ES10 isn't the brightest of cans either, so YMMV. I thought mids rich and highs non-fatiguing in the least. In fact, this combo is probably the least fatiguing configuration I've had so far. I've listened to the pair for hours on end since I got the player, I never felt any fatigue.
The player is also a joy to use. The touch-screen is reasonably reactive, things are very fluid and I never felt it was sluggish so far. The VERY nice touch is the hardware buttons on the side, for playback functions and volume. I haven't yet tested video, FM and the like, so I can't comment on those yet, since my primary purpose with this thing was essentially music. It's quite an expensive PMP since it does nothing else but that or almost, but that was precisely why I wanted to get it :P I don't need games, apps, whatever else, in my player. Just the best possible sound, and to me it's a clear improvement over what I've heard or had before. Well worth it, even if, admittedly, there are limits like no FLAC and no gapless. But I'll survive both nicely.
Feel free to ask for precisions if you'd like some.