Feature:
128 voice polyphony. USB key feature is really good, and the rhythms are useful for practicing. The display is really visible by day and night (gigged in both situations already). 32 setups make it easy to have a set of sounds cued up on each of the buttons, with levels set and everything. I wish there were dedicated volume sliders for internal and external sounds... you have to flip back and forth to set levels, which makes layering on board sounds with external sounds a bit more work on stage. But the killer feature for me is 36 lbs. Super light. Oh and the assignable buttons above the joystick are convenient. They are set up with octave above and below effects by default.

Quality:
I have a ton of Roland stuff that has held up amazingly well. I bought my first Roland synth used over 20 years ago and it still looks and functions perfectly. My old RD-300s is a tank and has taken 19 years of semi-pro abuse. I fully expect this piano to last me a long time.

Value:
The GX is a big step up in features from the SX, which is also a great board, but the superior grand sound and the display makes a difference. $1495 is a lot to pay, but you're getting great action that's not that different from the 700gx in my opinion, yet 20 pounds less weight. Going by feel, this is up there with S90, top end Korgs etc. I found a used one so got an outstanding deal.

Desirability:
I have been inspired to play it constantly since it arrived, and the action is just right. I was almost laughing out loud when I loaded my gear for the first gig with it. It is HALF the weight of my old piano. I literally put the gig strap over my shoulder and carried a synth case at the same time. I don't know how sexy it is, but there is definitely music gear dork love going on here.

Sound:
Superior Grand is pretty superior. When I first heard the sounds, I thought they were dull but then discovered if you set the Key Touch to "light" instead of medium it sounds much more natural and bright to me; it fixed everything. Odd that this setting is different sounding than the 700gx. The EP's are decent, organs are okay, strings are great. The RD drum kit is really good. Many of the general midi sounds are junky. For me, though, 90% of this thing's job is to play a good piano sound and they've got that covered.

Ease of Use:
Really easy to use the keyboard. Writing the setups took a little figuring out at first. The manual is not very detailed, as usual for Roland. Having used it live, it really makes my life much simpler. Changing sounds and levels, even layered stuff, is not difficult. I haven't used the USB key yet to trigger mp3 samples, but that will be useful for sound effects for me.

Support:
They covered a replacement key assembly for my JV-80 as a warranty repair-- 14 years after I bought it! They should win a medal for that. I've called them for parts and they were great.

Overall:
If you lug your own stuff and gig out, this is an ideal piano. Roland's quality and product design is outstanding. The main thing: superior grand! I plan to keep this for decades for live use and for recording/rehearsing in my home studio as well. It is perfect for me. The other one I was considering was the Nord Stage which is also light and compact but the interface is foreign to me, the action is not as nice and it's $3200 (organs are off the hook though). The 700gx feels and sounds a bit better but I couldn't stomach 20 extra pounds (and $1000 extra dollars).