This is better than I thought it would be. I used epic willpower to get through Justice League - the main problem was too many characters I not only had never seen but whose stories didn't mesh that well. When I heard how many of Marvel's characters were in this, I thought it might be a hot mess. It wasn't. They did a good job keeping the momentum going, and it wasn't too choppy. You will need to be familiar with a bunch of the Marvel movies. I'd recommend at least watching the first Guardians of the Galaxy, Thor Ragnarok, the most recent Avengers and maybe Dr. Strange if you want a better understanding of his powers and how they work. I'm pretty sure they'll be critical going forward in the sequel to this based on what was revealed so far.
I'm a fan who appreciates the lighter turn of the super hero films. I say that because it seems there are some fans who prefer the more serious vibe, for instance, those that criticize Thor Ragnarok for being too flippant a film. Understandable. Though I feel the newer DC stuff - on the big screen in any case - has gone too broody. Batman makes sense to be broody, that's his thing. Superman just feels weird to me if he's not this super earnest do gooder. I guess that's kind of why I like him. He's unrepentantly cheesy. Feels like we should have at least one of those dudes flying around out there.
Marvel has gone the other way, and Infinity War feels like a culmination of that. I like the jokey take and the various amusing pairings that go on in Infinity War. And I think it's possible the Russo's are better at this than Whedon was in Avengers (1). This had me chuckling more that I expected to be. Even the crew of Guardians of the Galaxy are sharper here. At least, sharper than GotG 2.
I think I'd give this five stars if it didn't end where it did. I, somehow, went into watching this not knowing it was only part of the Infinity Gauntlet storyline. That's frustrating, though I guess the story is big enough to merit two movies. I just felt blindsided by the end. I'm not a fan of cliffhangers in movies.