The Mac App Store
Maybe this is a naive point of view, but I can't see the value proposition for third-party devs to have their software in this store. Maybe I'm wrong and it'll be huge.
Launchpad
A touch interface for a screen that isn't touchable. Anyone I know that doesn't use Quicksilver or Spotlight uses an application stack in the dock. Nifty eye-candy feature, but I'm not seeing the usability gains.
Full Screen Apps
Not bad, but there are very few applications I want to run fullscreen at all, and even fewer I want to run fullscreen all the time.
Mission Control
Exposé, except there's a spaces overview at the top. A minor feature bump. Oh, and you can access the dashboard with it.
I understand this is a preview intended to excite people who aren't geeks, but still, it just seems so anticlimactic.