Iron Man: The original, no one thought it was gonna be so good and kickstart a whole big universe.
The Avengers: It fulfilled Iron Man's promise and kicked the MCU into high gear.
Winter Soldier: The peak, probably never to be surpassed.
Infinity War: Personally I think it was dissapointing, but it was the climax and where they had intended to lead to in the first place. Road has been patchy and uncertain from there on, including Endgame.
Last finished: Activision Anthology (PS2) (Patches+Unlockables): Barnstorming, Chopper Command, Stampede, Grand Prix, Megamania, Pitfall!, River Raid.