I've always found the sound to be a bit synthetic and plasticky, if that makes sense, but have been holding out in the hope that they'd improve things. I wish Pheads would have concentrated on improving the sound of the instruments rather than giving us something that seems to be an admission of failure ie - Combinator - Sure, I can see it's uses; but it seems to me that they are saying 'OK, Subtractor and FX, etc aren't that great on their own but look! you can chuck a bunch of them together and now they sound cool!'
It's a shame cos' I like the way Reason works but I just can't get past the underwhelming sound quality