So far the way I see it is:
Leopard Exposé > SL Exposé > Mission Control
I loved Exposé in Leopard, there was nothing wrong with it. It was quick, responsive, snappy, non-intrusive. It only changed the sizes of windows when necessary, and used up 100% of the space.
In SL, the windows are smaller, they and do not preserve their locations and relative sizes. I like that you can enlarge them with Space, but that's not an excuse for making them smaller and appear in random order. Also, Exposé in SL is slower, choppier, laggier and buggier.
In Lion, Exposé has turned into some random mess of icons and thumbnails everywhere, ordered arbitrarily and windows STILL hide each other because they are grouped together by application. There is just so much wasted space it makes me sad.
Apple: Bring back Spaces and Exposé EXACTLY as there were in Leopard. Forget the stupid Mission Control, please!