Bryan Singer's X-Men, X2, and Matthew Vaughn's X-Men First Class are far superior films to the Avengers.
They have better filmed action, better music, better drama, and more fleshed-out plot. I am surprised at the level of praise this film achieved, particularly towards Joss Whedon, when this film was so fast-paced and lighthearted, despite themes of global warfare.
This film was fun, but it felt very rushed and I don't think any of the characters got their due.
I also am not a big fan of SHIELD and do not understand their appeal.