Bumping for awesomeness.
Haven't beat the game yet, but I finally got around to buying this the other night. Absolutely love this game. The art, special effects and physics effects are all top notch. It's great that they kept local co-op in tact, as we were able to play (up to three players) on one computer, needing only one copy of the game. There's two co-op modes, unlimited (anybody can be any character at any time) and classic (pick one character). Unlimited became really easy as my brother and I would both be wizards and just levitate each other to objectives or across chasms. This of course led to us intentionally trapping/killing one other as we raced to get the XP orbs.
As for what's changed, gone is the magic meter (yay!). No more hunting down blue bottles to fill that up, a very welcome change. In fact, the only things you pick up are XP, either as floating orbs or bottles. It seems as though items are also gone, and in their place you have collectible paintings and poems locked in chests. I like the change though, the puzzle and combat aspects are the sole focus, and it works out well.
A fantastic game for $15. I'm liking it more than Portal 2, and I loved Portal 2.