I hadn't heard about hidden treasure in the hard setting! I'll have to check that out!

Rescue Rangers was an excellent co-op game (you could choose either a one-player game with either chipmunk or a two-player game with both). That's part of the reason I want that remake so bad: it would be nice to be able to play with my sister or a friend.
Rescue Rangers also stole a little from the Mario series (the level select map was VERY similar). So it has the same feel as a Mario game (while Ducktales felt more like a Mega Man clone LOL)