According to Disney+, 23 films belong to the MCU’s Infinity Saga, which revolves around the Avengers Initiative. The Avengers, a team of superheroes like Iron Man, Captain America, Thor, and many others, were assembled by Nick Fury to protect humanity from unknown threats.
The quality of the films varies, sometimes heavily depending on the main hero of the movie. I personally found the Iron Man films quite cool, and the spin-offs centered around Thor are also entertaining. Captain America’s missions are okay; I’m just not a big fan of Captain America. While Guardians of the Galaxy Vol. I is decent, Vol. II is not my cup of tea at all - even though I’m a science fiction fan. I won’t go into every single MCU spin-off, but none of them were bad and they were all definitely entertaining. Doctor Strange is another very positive entry for me, probably because it vaguely reminds me of Inception.
And then there are the Avengers films, which are about the team as a whole and the major threats to humanity. My girlfriend put it nicely: the films are chaos. While the first one already had a very dense plot, the subsequent installments didn’t get any better. On the contrary, the plot was split into even more threads. A lot happens, simultaneously, sequentially, separately, and together. I struggled to follow the plot and, consequently, the arc of suspense. More isn’t always better.
I enjoyed watching the films. They aren’t masterpieces that you absolutely have to see. But they are entertaining, and they create an overarching plot without constantly leaving you on a cliffhanger. If you don’t want to watch all the films, then skip the later Captain America installments. Ant-Man and Black Panther aren’t that great either, but then the Avengers films become confusing (as you won’t know the protagonists, and they aren’t explained outside of their own movies). The same goes for Guardians of the Galaxy. Though you can skip Vol. II without missing much.
The success of the series is not surprising, however; the films are well-made and have both action and a decent dose of humor. The comedic touch and brighter colors clearly distinguish the Marvel films from the darker and almost depressing movies from the DC universe, especially Batman and Superman, but also Justice League.