Well put together, good origin story, decent feel for the period, good actors who understood their jobs, appropriate appreciation of the tech involved, and a refreshing lack of modern political shibboleths. Cap was there to kick a ferocious amount of Hydra ass, and much Hydra ass was accordingly kicked.
*The ranking is:
X-Men: First Class (although this isn’t really an Avengers movie. I think)
Iron Man 2
The Hulk (the Edward Norton one)
Note that I’ve yet to see an Avengers prequel movie that I didn’t actually like.