For me, the part of this movie that pissed me off the most was the end. I don't need Cap or Iron Man to die, but I want to feel like there's some gravity to the situation I just watched unfold, and before you say "but Rhodey was paralyzed." No one gives a **** about Rhodey; Marvel doesn't even give a **** about Rhodey, that's why they tried to convince us that Terrence Howard and Don Cheadle are the same dude. Also, I know that the same could be said for Maggie Gyllenhaal and Katie Holmes; don't crucify me, it was a joke.
Suffice it to say, when I say "the ending," I mean "the actual, very, very ending, before the credits." They had the potential to turn this into the "Empire" of the Marvel movies, but they opted to play it safe in the name of keeping up the status quo. That letter was the most anti-climactic thing ever, and it totally undid Zemo's plan, which was probably one of the most interesting things to come out of the whole movie. You get that amazing conversation between he and Black Panther, and then you get him smugly rubbing Everett Ross' nose in the fact that he succeeded in sowing the seeds of dissent within the ranks of The Avengers, and you're like "this is awesome," only for Steve to send Stark a letter that's basically just the first few verses of "Ain't No Mountain High Enough," that amounts to "/JK We're still bros, right? See you in the sequel!"