I don't think Batman would do so hot in a normal Milsim game. However, as many have stated, zombie game or something else would work and probably fit in with the setting. It has to be a game with a lighter attitude such as a skirmish.

What I'd really like to see is this at a World War II style event.

http://dailypop.files.wordpress.com/2011/05/capwwi.jpg

The question is who would be Red Skull?

Exactly.

I already know a player that would jump at being on the Jokers team.

One time a guy came to trek in a kickass (from the movie) jumpsuit. It was neon green and yellow. It was a good day.