I've been running Unity for 24 hours now, and I can honestly say it's been the best desktop experience I've had in all my years. Notice I said best "desktop experience", and not "best Linux desktop experience". I have been running Windows since 3.1, Linux since Red Hat 5.2, and OS X since, well, Leopard. Unity is by far the best and most cohesive experience I've had so far. It tops OS X by a wide margin...it has many of the same sort of niceties with window management that actually makes sense (yes, I think OS X window management is horrid). Add to this the fact that it bakes some of my favorite compiz features (grid plugin anyone?) in and I couldn't be happier.
I know there will be some naysayers...many, in all likelihood, but in this daily Linux desktop user's eyes, Unity is a VERY big win for Ubuntu.