1) You can solve the rest of the Riddler’s riddles. Not a lot happens after you do that, but you do have to solve them to unlock some other weapons & challenges of the game.

2) Beat the rest of the challenges. These are battles that are very similar to certain key points in the story line. You need to beat them in certain ways and/or times to get certain rewards. Haven’t finished this one yet, but it’s fun to fight some of your earlier battles equipped with all of your bat-weapons and your mastery of batman’s moves.