To be as devil's advocate for a moment, Unity isn't half-bad as a UI. It only sucks if you are trying to remote into it because of how flashy it is.
I still don't use it because... let's look at Windows for a minute. Microsoft didn't try to be a Mac OS X clone, instead they applied their own design ethos and are forcing developers to follow it or forever look liike an old, stodgy MS app, which quite frankly is the way I like it.
You must remember that Unity is optimized as a tablet-friendly DE, as such, it feels like you should use Ubuntu on a tablet. Same thing with Microsoft Metro / Modern UI, since tablet computing is most certainly the way of the future, and convertibles aren't going away anytime soon.