You know what? It was just something about the 2nd level! I think it has to do with the game moving the first person POV around rather than me: too much unnatural or uncontrolled movement, and I can't handle it for some reason. I did finish the rest of the campaign yesterday with no problems! :D And I totally guessed the ending. ;)

Oh dear fuzzy, I can't even let myself think about Halo... I am SO excited about that game. KEYES & THE MAW WILL BE BACK! And 343 Guilty Spark. And The Library. UGH! I just can't wait to play all those levels again. And again. And again! AND THEN THE MULTIPLAYER MAPS! Eee!