I've read good things in reviews about the co-op experience in Lara Croft and the Guardian of Light - specifically, that the puzzles change to accommodate both characters with their unique abilities.
Does playing co-op really change all the puzzles so that they require cooperation, or only a few select ones? Does this include the skull tombs? Does anything in the game change except for puzzles - for example is the combat more difficult, now that there are two gun-wielding players?
Finally, what happens when one of the characters dies?