The keys are somewhat light so this is probably very playable even if you're not a pianist. I've played the piano all my life and to me this thing feels great! The action is inspiring, like a real instrument. I've recorded a few tracks on it already and the dynamics are exactly the way I would want them to be.
The build quality is great, keys faders and knobs feel good, but be warned, this thing is huge and weighs quite a lot compared to normal keyboards (without hammers). If you plan to move this thing a lot, that might be a problem. The casing is also quite tall, compared to a normal keyboard, which is very noticeable if you set it up on your desk. Doesn't bother me though.
The hammers are absolutely worth it. Playing with expression works great, it picks up on all the nuances as it should.
I use Ableton and it integrated seemlessly into the DAW, plug and play. I have yet to try out all the aftertouch stuff as I am new to synths, but as far as I can tell the amount of features plus the build quality you get for this price is totally fantastic. I'm very happy with this new addition to my bedroom studio. :)