I was doubful at first, thinking it was a very bad choice putting Renner as Hawkeye, but after seeing the movie, he is quite decent as Barton.
Cap may not be as strong as Hulk, or can fly like Iron Man/Thor, but he is the one making everything work, he is the center of the group, the tactician and strategist, who comes up with the succesfuland efficient gameplans (wait with the takedowns until rd 2 for example).
It's all about Teamwork in the end.
It was one of the better Superhero-movies so far.
Looking forward to Avengers 2, where you will see a REAL tough villain, that also has an impressive bench.