There’s only two reasons why you must watch this film:
1. Action scenes.
2. To give a closure to all those years of Marvel movies you’ve been watching one after another.
Other than that, there’s no good reason to watch it. The film completely ruins its most iconic characters, making them a bunch of grownups acting like teenagers, and letting you know that in all these years they haven’t evolved, or learnt anything of importance. They don’t even overcome their past problems. The end shows you the characters acting like they did in the first minutes of their first appearances.
But if that is not good reason to say the film is bad… There are LOTS of incongruences. Minute after minute you hear or see something that makes, literally, not sense. And by the end of the film you end up confused, and not because “it was part of a plan” but because the writers didn’t know how to work the material and they just contradicted themselves in the entire film giving us an explanation of how “something” works, to later show us that actually it didn’t work like that…
Also… For a comic book it’s cool to see a “deux ex” once in a while, but in a film is actually annoying. And this movie is horribly full of Deux Ex at a point that you just lose interest in knowing what power limits will have some character because you already know they’re going to change that at convenience.
So, if you’re expecting this to be a “Master piece”, and you are that part of the audience that actually pays attention to what’s happening on screen, I have bad news for you…