I don't think DC characters are inherently inferior to Marvel (although I've always preferred Marvel personally.) I think it's more that Marvel Studios is actively ensuring that the movies stay true to the characters.
It's very striking how the movies they're involved in feel far truer to the characters and the comics than ones where another studio is also involved. Even if the movies are good -
X-Men - there's something off about them that I can't quite put my finger on. But the latest
Hulk, Iron Man and
Captain America are right on the money. Marvel Studios on their own would never let some director like Ang Lee go galumphing off in some completely wrong-ass direction like he did with the first
Hulk movie. Maybe that's the movie where Marvel learned their lesson, that they need a firmer hand on the creative reins?
I think a lot of directors and studios might not appreciate the degree to which mere "comic book characters" have their own personality and integrity that must be respected. You wouldn't adapt
Hamlet and turn him into a cocky race car driver, would you? (I probably shouldn't say that out loud.)
But Marvel may have another advantage in that their characters do have "cores" to stay true to:
Spider-Man: with great power comes great responsibility.
X-Men: being oppressed is no excuse to be evil.
Hulk: basically the Jeckyl/Hyde story.
Iron Man: being a drunk with a heart condition is no excuse to be a bastard. (Okay, this one is more down to Robert Downey Jr's personal charisma.)
Captain America: exploration of "American values" in which the simplistic values of the 1940s are being explored in the first movie, with the 21st C due to expand the theme (if my guess is correct).
Compared with these, only Batman has a core theme: is vigilantism justified? But what's Superman's theme? "Truth, justice and the American way" is a slogan, not a theme. What does it mean? And isn't Cap covering that territory better anyway? What's Green Lantern's theme? There's probably a good one, I just don't know the character well enough. Bet the movie ignored it, didn't it?