I wouldn't say I'm very impressed with Lion: I don't find a big difference between Lion and Snow Leopard, except for Mission Control which I actually don't like at all.
I like Full Screen apps but I don't use them at all as they are buggy and they don't work well with other, non-full screen apps. Mission Control makes it a confusing mess. I'd rather have all my apps windowed, even though I like the concept of Full Screen.
I don't like Resume and I find it unpractical and annoying, so I disabled it.
I hate the 4-finger pinch and unpinch gestures, they're hard to do. I like Launchpad, but without an easy gesture, I can't integrate it into my workflow.
I don't like the bugs at all, and there are loads. Many more bugs in Lion than there were in Snow Leopard at release time. Things like keyboard input randomly not working, gestures not working in all apps (even the same gestures that used to work no longer work in some apps), etc... are very annoying.
I truly hate the new Finder organizing methods (Arrange By) and I hate that the old, better method (Sort By) is now only available if you press Alt. Yet another bug here, is it won't work if you first open the menu and THEN press Alt, you must press Alt before opening the menu, otherwise it does Arrange By even though it says Sort By.
I like the disappearing scrollbars, the gestures to switch from one desktop to another, the "group files into folder" feature, the new look of buttons and windows, and the fact that windows reopen when you reboot. I also like the Safari zoom feature, as well as the new Preview and Quick Look interfaces. I like Natural Scrolling a lot, though we should be able to set it off for normal mice and on for the trackpad independently.
I don't like how, when switching from one desktop to another, the menu bard and the desktop icons don't get carried over but reappear. They should simply stay put, as well as the background picture, and only the desktop contents should move. The menu bar, the icons, the dock, and the background picture (not necessarily, but why not) should all stay where they are, just like in Spaces. It makes more sense: your menu bar and icons don't change from one Desktop to another.
The new Mail is amazing, and iCal has some nice tweaks, but nothing special. I like the new Safari features, like the Reading list and the Download popup thingy.
Overall, there are more features I like than the ones I don't like, and most of the ones I don't like can be disabled, except for Mission Control, unfortunately, which is a major annoyance.