I've had one a few days now... (on loan)
There are some really good points, and then there are some really bad points

But at $895, some of the bad points are less deal-breakers than they might be.
Pianos... great. But except for the UltimatGrand, a little metallic at higher velocities. But I have a feeling that most Yamaha piano fans would like them... sparkly and mix-cutting, but with more depth to the sound, IMO. UltimatGrand is based on my G70 piano sound, and for me is the better balanced one.. 32 piano sounds altogether (plus some canvas stuff in the GS bank), but you're off your rocker using anything but the main ones!
E.Pianos... very great! something for everyone. Chunky Rhodes (3-ways), in everything from old 68 style to newer Dyno-My-Piano crisp. Pretty decent Wurli, a bit better than my G70's, actually. Lots of FM type and layers. Again, there's a preset for just about anything you want. Clavs, good, harpsichords, good (but I could do with more variation).
Now some bad news. Organs... terrible! There are a couple of things working against these. Firstly is the samples themselves. Most are derived from older Roland products, back in the day when there was no Leslie sim as part of the Canvas palette. So most of them have some Leslie sampled into them, usually slow. The problem now comes when these already Leslied organs are run through the GW's effects, which DO have a Leslie sim in them... A slow Leslie, out of sync with each note, being run through a fast Leslie

Yuck!
So I went through ALL the organs, and yes, there are a few without any sampled Leslie. But those, the factory MFX Leslie is set up pretty poorly. You CAN edit it and save a User Tone, so all is not lost, and you can set a fixed velocity for the part, so you don't get velocity sensitive organ (so wrong!). You'll need an expression pedal, though. There are some boneheaded voicing decisions here (more on this later), including slathering chorus onto an organ sound after it has already gone through the Leslie sim

The default parameter settings for both Leslie sims (one regular, one VK - a bit more mellow) are just terrible. You can do a LOT better editing these.
By the way, on the Latin GW, some of the better B3's are in the 'World' category. Some of them have slow Leslie and change to fast when the mod wheel is raised, but this has little practical use, as the paddle wheel is sprung, and can't stay on fast. Some of them have extra drawbars that get added when you push the lever... same issues there, IMO.
To be honest, OK, I did, with quite some trouble, manage to edit a few to usability, but I had to throw away just about ALL the factory programming, audition them carefully to find the few that DIDN'T already have a Leslie sampled into the sound, and completely reprogram the Leslie sim so it wasn't plain horrible (lessening the 'spread' value helped a lot). This area of the sound just goes to illustrate how piecemeal some of the soundset is. Some of it goes back to Canvas days, some SRX, some Fantom, some Sonic Cell. But there's little consistency in the programming, and some obvious clunkers due to CC's being needed to control the sound that the GW just can't provide, live.
So, a push... With work, it's usable, but nothing to write home about...
Guitars... OK, first, I'm going to talk about something else.

It baffles me just how inconsistent the effects programming is on MOST of the GW sounds. One guitar will be nearly bone dry, and one will be drenched in reverb, another will have a tiny room, another some timed echos, but not much of it is related to the sound. For me, personally, I would have to go through all my favorites, load them into a Performance, and save those as 'Favorites'. It's just not what I'd call a very 'consistent' sound set. Pull one sound in from the Factory ROM, and you are likely to have to dive for the volume control or effects knobs in a hurry.
Now, for someone using a Sonic Cell in a WS environment, where everything is set up in advance and the controller likely DOES have enough knobs and levers to control the voice, this should be no problem. But in something this preset, it's a hassle no doubt.
OK back to guitars. Acoustics, very good, especially with a whole extra bunch in the "world' section, including a gorgeous 12 string, and the most playable mandolin I have ever used. Straight notes on the keys, raise the lever, you have a nice tremolo. With practice, it's uncanny! Good resonator dobro, too...
Electrics cover all the basses (

) The MFX distortion helps a lot here, but again, you have to watch out for volumes. Not a very consistent batch. Quite a few with 'dive bomb' down bend ranges, but that CAN be defeated in a Performance.
Basses cover all the basses

In fact, a lot better than my G70. Fat finger basses are MUCH better (I simply HAVE to break down and buy SRX-07 for better basses one day!), acoustics are good. Pick basses good (although, at times I almost felt like there was TOO much lows, but that's fixable). Fretless, synth basses, all good, all usable, all with room shaking bottom (that's much improved over the G70).
Strings... Good violin and cello (better than my G70) but darn near dry. I just can't stop thinking 'what drugs were they on at the voicing team?' Other than that, your pretty much set here. Marcato, staccato, pizzicato, big ensemble, small ensemble, Woodwind layers, big layered tutti stuff. I could probably do a decent classical score with some work... My favorite sound is to layer a medium string section with 1260 Vn+Va+Ct. - smooth, but with a bit of bite and detail to the line.
Woodwinds... not great, IMO. Very little choice (but some better flutes in the "World' section, including a great SingingFlute for the Tull and Focus fans!). Enough to get by, but not stellar.
Brass, not great again. I miss my SFZ Brass from the G70. Again there's a bunch more in the World section, but it's heavily weighted to those awful Latin horns with a vibrato that would kill even Burt Kaempfurt! There's SOME good stuff there, but on the whole, it's weak, for a Roland (my G70 is better). Strangely, after the Canvas era great french horns, they're gone, and there's not much french horn variety.
Saxes, again pretty weak, IMO. Nothing close to my G70. (I got to keep saying to myself 'but it's $895!). Again, most of the best ones are in the World expansion section. Best thing to do with these is layer them with a brass sound and get a good section sound!
OK, synths... nothing but thumbs up here... Everything you could ever want, and then some! Roland, doing what they do best!

Some great arp stuff, but not tempo synced (at least not to the arranger - maybe SMF?).
OK, drums... much improved over the Canvas, but at a cost. Sorry, guys, but the days of GS are GONE

You'll have to do some editing to get older SMF's to work with these. Foot closed HH is now half open (has been for a while, though), some toms are flams, some are velocity switched flams, the handclap on D# is now a 'ghost' snare note/roll. Nothing I haven't had to deal with on my G70's V-Drum kits, but be aware when plugging in older SMF's...
Great selection of different kits, lots of vel-switching, great dynamics. Then there are some great menu kits, every snare, every hi-hat, every tom, etc.. But still no USER KIT. So using these in a style means picking one kit and sticking to it. Which is a shame because... in the World section there are some GREAT latin kits and menu kits of just about everything you might need, including (drum roll please...) finally a back and forth tambourine, which GS guys have been waiting for a LONG time! The latin stuff is GREAT (as it should be!) But in Style mode, good old Roland STILL only give you ONE drum track. So if you want those latin percussions, you have to use a Latin kit that has some of them (there are too many to even fit in one kit!).
This is one area where the Sonic Cell roots show badly. As an SMF module, this thing shines. You can have multiple kits. no problem. But style mode is more restrictive. Roland better give us either multiple drum tracks, or User kits, or both, pretty soon!
But, overall, thumbs up to the GW drums, and the styles definitely show them to their best. Great dynamics, detail, punch, in your face!
Well... that's the good news... mostly.

Next up is the operational aspects.