It's different though. Marvel seems to do quality control on their comic movies as a group (iron man, hulk, thor, capt. america) while dc seems content to license their franchises out to whoever wants to make them. It's resulted in a great success (read: Nolan), but other than that it's largely flopped. It's an old problem too. The early Superman and Batman film franchises had the same problem towards the end: garbage movies that were created solely to make money, as opposed to telling a decent story.
Really DC just hasn't done much besides Batman and Superman. The first two Superman, The Dark Knight stuff Mask of the Phantasm are all fantastic the Tim Burton Batman movies were great at the time too, and they still have the best comic book atmosphere. Other than that stuff from DCs vertigo brand (Watchmen, Constantine/Hellblazer, V for Vendetta, A History of Violence, The Fountain, Road to Perdition) are excellent stuff.
Marvel has done more movies with their actual stable of "superheros" but I think they have had the same problem with cash grabs and declining quality after a couple movies. IMO It happened with Blade and Spider Man. And DC and Marvel have both had some stinkers. For every Catwoman there is an Electra (although Halle Berry and Jennifer Garner
).
I still need to see Green Lantern, don't really know much about the comics besides there are green lanterns for every sector of the universe or something.