I don't have high expectations for this movie. The big crossover movies tend to be among the worst MCU movies in my opinion, just because they have to give every character their own storyline instead of focusing on the story the film is trying to tell. Based on the trailers I have seen, this movie seems particularly at risk for this trap.

For some reason, the Fantastic Four are going to meet the main MCU cast, then you know they will fight until they see the goodness in each other's hearts and become BFFs. Then the X-Men will show up, possibly as Doom's minions or something, and the same thing will happen. Also, Captain America is back! There is going to have to be a plot line about why he leaves his world and how all the Avengers are happy to have him back.

Let's say the film will start with 30 minutes for the Avengers to assemble, then a half hour for each of those stories, and suddenly, there are only 60 minutes out of a 3 hour movie to tell the main story of Dr. Doom/parallel universe Tony Stark trying to take over the multiverse or whatever his plan is.

Am I still going to go see it in theaters? Probably. I am sure I will have a few friends who will be dying to see it and will want to go see it in a group. Plus, I am sure that it will have a couple amazing set piece scenes and it will be referred to by every MCU film for the next 2 years.