There's a ton of stuff going on with the Yamaha Motif XS7! I've used older models of the Motif, so adjusting to this newer model wasn't too hard. I've really only used it a few times so I didn't get to check out all of the new features it has but was at least able to use it for it's most basic functions. The big upgrade is the LED monitor that's now a lot more visible and more in depth with what you can do with it - it's also the thing that's going to take the most time to get used to when compared to the older Motifs. Even if you haven't used any models of the Motif, it's pretty intuitive to use. However, like any in depth workstation it's going to take some serious use to learn all the ins and outs of it. The manual will definitely be helpful in this endeavor, but not necessary for more basic usage.
The sounds heard from the Yamaha Motif XS7 are quite good in general. However, I don't see much of a different in quality or realness when compared to the older models of the Motif. It does have more sounds in general, but your basics like the acoustic and electric pianos, organs, and the like aren't a huge step up in my opinion. I understand that if you get the XS7 that you're not really buying it for these basic sounds but for it's more in depth controls and features, but that's pretty much what I've used it for...
It's hard to go wrong with an instrument like the Yamaha Motif XS7 as it has so much to offer. However, I'd highly recommend checking out all the major workstations like the Tritons and Viruses and the like as each of them are different and bring different good and bad qualities to the table. The XS7 is really cool but I don't know if it's the best overall choice if you're just looking for sounds, in fact, I'd say it's not. If you want to work all in one workstation this will do it, but with DAW's there's a lot better ways to go about it in my opinion. Still, the Yamaha Motif XS7 is a great workstation that's worth of investigation at least for those in the market for an all in one workstation.