The one real fault is the almost complete lack of exposition, and whilst the previous movies cover that for the Avengers themselves, theres not a lot of back story for the mutha of all baddies or even his "children" captains. So much like Lord of the rings/Harry Potter Part 1/2, its not intended at all as a standalone movie, but that must be obvious to anyone with any knowledge of the Marvel Universe. That aside, awesome for fans.
Gamoraaaa!

5 stars. The unfortunate downside is that this will clog up multiple screening rooms in each cinema for a good few weeks to come.