This movie could have easily lost an hour and still gone on a bit too long. The first quarter of the movie is them splitting up the gang so that they can get the gang back together, then the gang finally does a thing together, then more of the gang shows up, then we spend a lot of time saying goodbye to the gang.
Not to mention how hard they have to bend over to explain why Superma-- I mean Captain Marvel can't just easily solve all of the big problems herself and also why she gets a haircut. Then she shows up again to basically solve the problems herself.
3 hours is a long time to spend on an inevitable conclusion: The Avengers beat Thanos. Surprise! They do exactly that. I guess maybe there's some excitement to be had in guessing which actors are tired of doing these movies all the time.
The best part of the movie is when it's over and you get a break from it. Wouldn't it be nice if we all did from these movies for a while.