I've been using Lion for a good while now and I can tell you that:
1) Launchpad is useless. you'll try it but never use it again.
2) The new Spaces are terrible and plenty of bugs (if I have a finder window open in space #2, and want to go back to space #1, it immediately returns to space #2 and puts the finder window upfront. then i have to close it, in order for spaces to accept to go to space #1).
2) the new finder with gray icons is very confusing. with the colored icons in snow leopard, you could distinguish very quickly if you were on the downloads folder, the app folder or the documents etc. now its all gray, and you really have to spend a few seconds there to find what you want. they also changed the orders of the icons. all this = terrible changes. it will confuse people.
3) why is the new quickview white, again? why can't it be transparent? the only good thing is the fullscreen - but if you're viewing one picture out of a folder with several other pictures, the arrow keys on your keyboard won't help you navigate - meaning you won't be able to change pictures - you'd have to get out of fullscreen, click the arrow key to change the picture and go back to full screen. AGAIN, useless.
4) scrolling gesture is now inverted. it's not touch screen, so why is it doing like an iPad? Im not touching the screen, so it doesn't make sense. if i was touching the screen, it would. everytime you try to scroll down and the window scrolls up, feels like I'm being trolled.
There are plenty more rants, and I can safely say Lion is a bad update. At least from my experience. Snow Leopard is far superior.