It feels a bit picky to complain about a movie that succeeds on so many levels. It probably deserves the $1.9 billion and counting that it has collected at the box office. It ran for 2 1/2 hours without being boring ... the only break I took was when my old-man body had to pee (thanks to the great app RunPee, I knew when to go and what happened while I was gone). And some of my complaints are personal, based on taste preferences more than anything concrete. (As an example, I like non-stop action movies when they feature actual human beings ... The Raid movies, for instance ... but am not as impressed by movies where the action is largely CGI superheroes flying around and beating the crap out of each other. Or, as I said about The Last Jedi, "lightsaber fights are boring, especially when you consider what is being done in movies like The Raid films.")
Infinity War has more emotional depth than is usual for these movies. Josh Brolin as Thanos in particular is more than just another Big Bad. But at some point, enough is enough. (I realize that any movie that makes close to $2 billion clearly hasn't reached saturation for most people.) Because Infinity War is partly the culmination of previous films in the Marvel Cinematic Universe, a large number of important characters turn up. This is especially the case with the Avengers and the Guardians of the Galaxy, who meet up and instantly double the number of key characters. (Not to mention Black Panther, Dr. Strange, Spider-Man, and others.) There are simply too many characters in Avengers: Infinity War. Crucial characters like Black Widow (Scarlett Johansson, 5 minutes screen time) and Black Panther (Chadwick Boseman, 4 minutes) are barely around long enough to make an impression. (If you're a fan of Hawkeye, spoiler alert: he's not even in the movie.) Then there are the actors, some of them truly great, who were in Infinity War and I didn't know it until I saw their name in the credits: Idris Elba, Benicio Del Toro, and Carrie Coon come to mind.
Having said all of this, I can safely say that if you are a fan of the Marvel Cinematic Universe, you will like Avengers: Infinity War. You will probably see it more than once. For me, almost all of the movies in the MCU run together ... I give them all the same rating, with the exception of the Guardians movies, which I didn't like, and Black Panther, which I think is a great film. This doesn't mean I don't like the movies ... that "same rating" I give them is 7/10. But I don't care about them in the way I feel I should about a $2 billion success.
I could best express my position in all of this by noting that my 2nd-favorite part of the MCU (after Black Panther) is the TV series, Agents of S.H.I.E.L.D.. There are people with superpowers on that show, but the reason it's still around after five seasons is because it has real human characters that you get to know in depth.