Feature:
This thing is PACKED with features. There is the audio interface with effects, the synth with nice sounds and loads of tweakability, it also works as a midi keyboard for your software, there are a number of pre-programmed templates so the large control section can be mapped to your VST's or DAW. Oh yeah, and it has a joystick and touchpad.

Quality:
Feels well put together. Every key and knob felt pretty solid. Also, I like the key-action. I travel a fair amount with it, though not regularly, and it has held up well.

Value:
For the money it's great. An all in one sort of thing to use with a DAW + laptop for a great mobile studio. I got my x-station 61 for $549, which was a great deal.

Desirability:
Looks great, does so much!

Sound:
The synth section of the x-station has some great sounds, and there are more free patches available on the Novation website. Unfortunately, the synth can only store 200 of them at a time, so you have to try them out and then pick and choose. The pre-amps on the audio interface are nice for the price you are paying. There are even a number of built in effects that are tweakable and sound pretty good.

Ease of Use:
Very easy to use. You may need to update the onboard OS but directions are straightforward. They get some minor marks off for requiring a third party software though.

Support:
Novation has done an excellent job of supporting this product with updates and even free sound patches.

Overall:
I may upgrade my audio interface sometime in the future, but I definitely won't need to get another keyboard controller ever.