They're okay, but you have to be with your child while watching the movie so you can point out language/words that are not nice to use or say to others. And how some actions are not good to copy in real life. - Mom of two boys who are Marvel fans! My youngest 21 months old, loves Iron Man and The Hulk. :-)
I think they're fine. I grew up reading Marvel and DC comics/graphic novels and they can be much more graphic and in your face compared to the movies and it never influenced me in any negative ways. The movies are actually quite much more watered down and kid friendly :)