Ultimate Avengers 2 is in the uncomfortable position that it is better than its awful predecessor, but relies so heavily on the elements from part one, that watching it in isolation is a considerable weaker experience than after watching the first one. That said, while it’s better than the first part, it’s far from perfect. The action and plotting is mostly good, taking the best from the first part and spinning it off into a new direction that had nothing to do with the second volume of the Ultimates comics (the first part was an adaptation or better heavy distortion of the first volume by Millar).
But the soup opera-style characterization, especially every time couples were involved (Wasp/Ant-Man, Banner/Betty), was still pretty bad. So, if you saw the first part and disliked it, you might still try this one. And if you liked the first part (what’s wrong with you?), then this should be perfect.