Alternately there is the risk he could play it like he plays Willy Wonka.
I'll believe it when they're in front of the cameras shooting the film but until then a tiny pinch of salt will accompany any of these claims.
As for Cher playing Catwoman, she's probably a bit too old to play a character as lithe as Catwoman but I have every faith in Nolan's ability to make a good film.
As for Johnny Depp as the Riddler, I think he's the perfect choice.
If they were to use "The Caped Crusader" as the title it would certainly fit in with Batman's redemption in the eyes of the people of Gotham which is where I would expect Nolan to take the film.
Give the man some credit, he's a better actor than that. He can do kiddie acting e.g. Willy Wonka, Pirates trilogy but can do serious adult acting when needed as well. E.g. Fear and Loathing in Las Vegas, Donnie Brasco