If you want brain-dead simple, feature-deprived but so basic even my 91-year-old grandpa could understand it, Lion has Launchpad. If you want middle-of-the-road in terms of usability, features, and ease of use, you have full-screen apps. Semi-advanced usage, hey, the Finder is still there, still confusing as ever to novice users and still frustrating as ever to the mega-geeks who crave UI consistency. As someone who knows just enough about power user features to be a danger to myself and others, Mission Control rocks my face off with its features. And finally, for the über-nerds, Terminal is the same stolid UNIX-y text interface it's been since the 1970s.
That's a great description of OS X Lion.