Good fun, great cast, self contained (mostly), cool Easter eggs, finally introduced the last 2 original comic book Avengers, and ultimately it's pretty funny and does not take itself too seriously.

I think the general consensus is still that the best 5 movies are, in some order, Iron Man, The Avengers, Captain America: The Winter Soldier, Guardians of the Galaxy, and Avengers: Age of Ultron... I personally really like The Incredible Hulk, and I think Ant-Man will ultimately fall in with that one.