The good stuffs are already covered on youtube. So heres some of the uninteresting changes at first look.
UX is totally different. For some it may be a disaster. Perfect example will be Clock; no features missing, but the moment you see the new app you'll feel the overarching need from designers to dumb things down, even when it's unnecessary.
Preliminary thoughts are that things are butter smooth. You get the OSX-like drawing windows animation when switching windows. Very very slick. However, if you tend to leave many apps opened, and many tabs in each app, for example several tabs in chrome and several in others, the new multitask window will be a mess. Maybe it's to be an acquired taste, let's see.
In settings, you can now see your ram usage. Nice.
Stock keyboard has a flat design now, so you get the feeling you're typing on the wrong keys all the time, quite interesting Google decide to head in this direction. Also because there is no longer a vertical line separating the buttons, the number pad on the QWERTY keyboard looks like a joke.
Couple of new wallpapers, which is always nice to have.
As a whole, I got to say lag is non existent which is a great feat considering this is next gen UI. Whatever google did, they did great.
Oh yes,check out the new battery history, theres a simple linear extrapolation to tell you how long more your battery's gonna last
