Got to see this on release night, and there was a general consensus among the group I saw it with that Black Panther seriously carried that movie. Or, more accurately, while none of the other heroes were bad or mediocre, per se, Black Panther was just a stand-out member of the cast that had AMAZING moments in the fight scenes, (seriously, dat triple kick was gold) and now I'm really looking forward to his own movie. The action itself was fairly superb, which is good, since that was the core reason I was there, as I am not at all caught up on the Marvel movies. I think every member of the cast also had their own humour style, too, unlike one of the big critiques I remember hearing and having for the first Avengers movie where everyone else was kind of just quipping like Tony. I can't really note anything I didn't like right off the bat, other than the obviously forced and very swiftly dropped (thank god) romance between Cap and Peggy's niece, and I definitely felt the Secretary of State was a dick consistently throughout the movie.
Also I do have to note that given how much destruction typically happens in these movies, it's actually kind of refreshing to have a movie that actually discusses the collateral damage rather than just leaving it at "city's in ruins, but the death toll wasn't absolutely horrible and we're not all enslaved so uh HEY victory for us!"