The Avengers has probably aged the most poorly of the MCU, in that it was great when it came out and now is kind of a chore to get through because you more easily recognize the lack of overall big budget directing experience that Whedon possesses. Jon Faverau or Joe Johnston would have done a better job.

As far as any controversial opinions that I have about the MCU, I think Doctor Strange's solo movie gets a unnessescary flack. It made me care about the character and his world for perhaps the first time, and I think had there been more scenes with the villain to flesh him out a bit, it would be among my favorites of the series. As it stands, even, it kind of is.

I also think Thor: Ragnarok is severely overrated. Love Taika, but he really went out of his way to make a more fan-fictiony movie than a Thor movie good on it's own merits. Thor's best movie appearances are easily Infinity War/Endgame for me, with the first Thor tailing distantly behind. Those movies seemed to get what works about him, and Ragnarok feels like it's about this entirely other thing that I care less about.