If you haven't seen the other Captain America and Iron Man movies I can see some people coming away thinking it's not "perfect" or "nearly perfect" as most of the reviews indicate, you can find plausible holes in some of the action and character motivation, but as someone who has seen every movie leading up to this, and read the relevant book, this movie gave me chills and left me speechless at several points.
This is probably the only movie that will ever tie so many character arcs together so intuitively. Quite frankly I can't see Marvel topping this performance ever again, the tangled web we're about to enter in Infinity War probably won't allow this much depth... "Probably".
If Doctor Strange turns out really good then who knows, Cumberbatch could work wonders for Thor and Guardians of the Galaxy. It's possible we're just lining up to have our minds blown all over again with new characters in the Galactic setting, but when it comes to Cap and Tony, this is the payoff, you aren't going to get anything better out of those two than what you get here.