http://www.apple.com/macosx/lion/
I think it looks pretty cool. I know the Mac App Store is going to make some people afraid of a closed system, but it's just an optional way of getting apps for your Mac. It's not the only way; it is still a desktop OS afterall (just with a few extra layers added). The App Store will make it easier to find apps and keep them updated, but (most importantly) it will re-invigorate the Mac desktop app market. This is clearly a win.
I really love the Mission Control stuff. Expose is already a huge part of how I use a Mac, this will just make it even better.
Launch Pad is cool. It will require a trackpad in order to really get the full iOS effect, but it's pretty neat. I'm still not sure if I would deviate from using Spotlight to launch everything... I guess I'll have to see it in action. I'm not a fan of how the open folders look, though.
Full-screen apps will be awesome. I mean, a lot of apps already have a full-screen mode built into them... but making it a simple function of the OS itself is very nice. Combining this with multi-touch gestures, and I can see switching in and out of full-screen to be really handy.