The MCU has done a great job bringing these comic book heroes to life but not the same can be said about the villains. The villains in these movies have been, for the most part, predictable and not memorable--outside of Loki and the Kilmonger ofcourse. Thanos has to strike fear into the audience, the threat of this guy has to feel daunting and authentic.
It's an Avengers film so you can expect it to be action-packed, but hopefully they took the time to put some great interactions in the film as well. Not only do audiences want to see these heroes on screen but want them to meet each and ultimately combine their powers. Can you imagine the killer combos that characters like Spider-man and Dr. Strange would have together? Or the hand to hand combat that the trifecta of Bucky/Cap/Panther could have? The possibilities and combinations are truly endless--we want to see them all!
1) Satisfying Ending:
So many films have been leading up to this that the climax of it all has to be of epic proportion. Anything less than that could be looked upon as a failure, audiences have to leave the film elated and hurt at the same time. There will likely be a number of deaths in the film and Marvel must remember to do these characters justice before they die, and not have them just “fade away” in a lackluster unimaginative way--*cough* The Last Jedi *cough*.