I suggest going to see it! You don't have to watch the first two, but if you haven't seen the Avengers you might be confused about things he references.
I love them all, so... I will recommend you watch them all!
We were going to see it, but most of the ones are in 3D. I don't like 3D movies- they hurt my eyes. Josh might go see it with his dad or best friend. I'll probably see it when it isn't as busy or when Josh buys it.