Avengers was a benchmark setter. Having rewatched it yesterday it's still fucking amazing. It's just such a satisfying movie that elegantly combines every character, instantly defines each and every one, and does the really cheeky thing of making "can this entire movie's concept actually work?" the basis of the movie's story. You want them so desperately to all be able to team up, everyone in the movie points out how it can't be done, all for that satisfying payoff of the iconic panning camera shot of every character and Silvestri's now iconic theme. Even now when I watch it, I pump my fists in triumph when that moment happens. The ending is just such an incredible encapsulation that gets me a little bit misty-eyed when I realize how the mad men actually pulled it off. "The Avengers are dangerous; every world knows this", and in Nick Fury's words, none of it was to make a statement - but to fulfill a promise.
Avengers 2 fails to meet the benchmark but it's still pretty good. If anything I have a lot of delayed appreciation toward many of it's scenes. "Less than the sum of it's parts" is a good way to describe it; just about every scene is great, capitalizing on character dynamics and personalities, but it is admittedly bloated under the weight of it all. Reminds me a little bit of The Dark Knight Rises; yeah it's all great but it's not exactly elegant.
That said, Bobvids' critique on CinemaSins' Everything Wrong With video actually made me appreciate Age of Ultron a lot more. It's a good watch that I really recommend if someone's a bit split on the movie since there's a surprising amount of attention to detail I never appreciated.
