Hm, the first look I had of it was a demo unit that was out of the silicon case. The build quality looked pretty good and the screen is nice and clear.
The odd buttons were rather unintuitive at first but I think I'm getting the hang of them already. The awkward positioning actually makes it easier to find the buttons without looking at them I feel.
The UI is clean enough but searching for songs was a bit of a pain, coming from touchscreens and alphabet based searching. That most of my songs are Japanese didn't help as the system automatically sorts them towards the bottom in no apparent order. This was improved with some filename jiggery pokery and arranging them into folders. Haven't fully tried out the other features yet.
As for the SQ, the first time i auditioned it i was blown away (coming from a Galaxy Note 2 with Fiio E06 amp) by the sheer clarity of the sound and the ease with which the X3 could drive my ATH-M40x (they weren't kidding about building in that E17). That was pretty much the deal-clincher for me.
After a few more hours using it though, I feel that the sound is very slightly lacking in body, though that's mostly due to the M40x's flat sound signature. Here's where I feel that having an equaliser would have been an improvement as the sound can then be tailored to the headphones. The X3 does allow for treble and bass adjustments but as the M40x is slightly lacking in the mids, I tried to drop both the treble and bass to relatively increase the mids but it wasn't quite as effective. Will try again with the higher gain setting tomorrow.
I also had the chance to test out the DAC function and the X3 was a strong competitor to my laptop's Creative Sound Blaster sound card. The native sound card just managed to edge out the X3 but I'd forgotten that I had enabled the equaliser and virtualiser. Will compare them again on a more level field when I get back.
All in all I feel that the X3 has truly fantastic value for the quality you're getting. The lack of an equaliser proved to be a small con to me but YMMV. I have high hopes that it will be included in the upcoming firmware updates however, seeing that it's in the (very beautiful) X5 and also how responsive JamesFiio is with regards to product feedback. =)
And thus concludes my first ever mini review haha.. I'm no audiophile and so I apologise for the use of nonstandard words in my descriptions..