If they nurtured and allowed the community of designers and hackers to create themes, they would probably have a good theme by now.

But honestly, I like the Mac style desktop. I use gnome even though it's probably the worst for power users, don't shoot me, but I honestly haven't seen a cleaner and functional theme that doesn't require hours of configuration.

We should have many by now. Still even linux is full of ms paint designed themes too it seems, so maybe I'm wrong.