It's like make-your-own-justice-league.
The superhero universe is a match made in heaven for MMO gameplay. City of Heroes showed that it was possible without any expensive license, it was about time that the comic book media involved (without getting cancelled) and soon we'll be getting the DC Universe Online on both the PC and PS3 this November.
Rather than having a city filled with Supermans, Batmans, Flashes, etc, you'll be still making your own hero. But we're still looking forward to it. Released at E3 was this trailer that refreshingly showed all in-engine scenes and some real gameplay.