In my opinion, there's something about the majority of the Marvel-based films that just capture the whole superhero 'theme' so well. I even really enjoyed Spiderman 3, which is often panned, as I really felt it still retained that quality, imo even more so than the second installment. Never really connected with the Hulk or X-Men films though as they were too based in some form of science-fiction thriller format for me to really enjoy them as superhero films. X-Men in particular I just felt tried too hard to create a sort of 'epic' futuristic war storyline.
I love Nolan's Batman films, however for me I don't see them as 'superhero movies' either. In that context I think Burton's films pull that off far better, however as dark, character-based thrillers in their own right Batman Begins and The Dark Knight are brilliant. What needs to be remembered with the next Superman film though is that he is not Batman - in fact he is probably one of the easiest characters to base a good, traditional hero movie around.
Too much to agree with there, but Spidey 3...really?
Now that you will find it harder to believe a man can't fly on screen, Superman is incredibly easy to do. The foundation of all super-heroes. Just don't keep harping on about the origin and camping up Lex Luthor.
Marvel just seem to have a lot more options in bringing their characters to screen, if in a minor way: Dr Strange, Iron Fist... very easy to work up treatments. DC heroes are very fantastical and can't be transferred on a small scale. Grant Morrison emphasised it with his "Big 7" JLA.
Iron Man always seemed very obvious to me in the 21st century - weapons manufacturer, government contracts, leading technology, wealth, SHIELD. What made it unassailable was getting an actor with the charisma and talent of RD jnr to play the role. Otherwise, Green Lantern.
The Avengers and its ensemble has brought 1960s Marvel comics to life - characters and story lines inter-connected to show a shared universe, the equivalent of JLU. Very ambitious and at any stage it could have fallen apart with great costs. The fruit has been what might be a mega-franchise with roots and off-shoots generating strong profits and awareness.