Don't know if my ideas are gonna be any good but here the are:
Daredevil: I think DD needs his own game with free roam, random crimes guest starring marvel characters, splinter cell-like and the radar thing and a hell of a fighting and acrobatic system.
Batman: Seriously a game that dosen't suck. A free roam game would be good for bats too as using th batmovile and else. A great fighting system and splinter cell stealth style. I think the stealth is good for both bats and DD. Oh and a great interrogation system but not as violent as the punisher game.
Punisher: His game was really cool, they deff need to do a second one.
Spider-man: I'm trusting the third game for the movie is gonna be great. But I still want a comic book based one, but not as USM that one was way toos hort and sucked.
Teen Titans, Fantastic Four, and X-men: I don't really like FF, XM or TT but my idea here is I think they could work great as role game play like x-men legends and include a little action mission based just to get the feeling of one character alone. X-emn legends was great but the x-emn movie games are practically wolverine's ones.
Flash, Green Lanter and Superman: The Returns game looks good for superman, but I don't want to argue wether or not is gonna be good. I want to see how they handle his super-speed if it's good then a flash game would be cool. As for GL I think his game would be complicated.