Coming from Lion, its pretty good.
Some of my observations that I haven't seen elsewhere...
- Most apps seem to load a tad faster, and the boot up was faster too.
- The light on the dock is different for apps that are opened, its not as easy to see, but thats fine since I don't use it much.
- So far all my apps are working.
- Swiping with the trackpad in the MAS now acts like Safari, instead of just going back or forward a page, it will show the new page in progress if you slowly swipe. Doesn't do that in iTunes tho.
- Mail now instantly opens in full screen mode(after opening it for the first time without it and going into full screen manually), has never done that before.
Those are my initial impressions from the past hour or two, may update if I notice more.