Honestly, I think Infinity War was the peak of the MCU.  
And I don’t even necessarily mean that it’s the best Marvel movie ever made. I just think it was the moment when everything the MCU had been building for years finally came together in a way that felt almost impossible to pull off.  
Like, think about it. You had 10 years of movies leading to this. Thanos had been teased since the first Avengers, the Infinity Stones had been scattered throughout different movies, and all these characters had their own stories going on. Then Infinity War comes along and somehow manages to put Iron Man, Captain America, Thor, Spider-Man, Doctor Strange, the Guardians, Black Panther, Wanda, Vision, etc. into basically one story without making it feel like they’re just there for the sake of it.  
And Thanos being the main character of the movie was such a crazy decision. You’re basically following the villain for most of the movie, and somehow you understand his motivation even though you obviously don’t agree with him. And the biggest thing is that he actually fucking wins lol.  
That’s what made the ending hit so hard.  
The heroes don’t just barely lose. They completely fail. Loki dies. Gamora dies. Vision dies. And then Thanos snaps his fingers and HALF OF THE CHARACTERS DISAPPEAR.  
I remember watching that ending and just thinking, “There’s no way they actually did this.” Especially with Spider-Man. That scene still gets me because Peter isn’t even thinking about being a superhero anymore. He’s just scared and doesn’t want to die. And Tony is completely helpless.  
And then you leave the theater with basically no idea how they’re going to fix any of this.  
That’s probably the thing I miss the most about that era of the MCU. There was this feeling that something genuinely huge was happening. You had been following these characters for years, so when everything finally collided, it actually meant something.  
The Titan fight, Wakanda, Thor arriving with Stormbreaker, Cap finally fighting alongside everyone again, Spider-Man and Doctor Strange interacting with the Avengers, the Guardians meeting the Avengers… there were so many moments that felt like actual payoffs to years of buildup

Avengers: Infinity War (2018) was the peak of the MCU