Mavericks will be a great release in my opinion... for laptops. There's not a st_tload of new features, but it feels like they worked very hard on what you don't immediately see, under the hood.
As a rMBP user, 10.9 feels faster, more stable, lighter and more responsive than ML in general. The battery lasts longer, the laptop seems to run cooler too. In overall, for 20 bucks, it will be an excellent product imo.
My only deception so far: I think they could have put more effort on the visuals. The skeuomorphism is gone, finally, but the apps aren't necessarily more beautiful. Game Center still has its horrible green felt look for example, Reminders didn't change, and the Notes app isn't particularly interesting.
I expect and hope for more changes, visually, when they release 10.10?!. Hopefully, they won't go full retard either and give us a dumbed down version of OS X, like MS did with Windows 8.
For laptop users, 10.9 brings great enhancements in my opinion, but for iMac and Mac Pro users, I'm not so sure