I thought it worked well before the first Avengers movie... Each hero had their own movie with no real continuity other than the post-credits scene, and then Avengers - and only Avengers - assumed you'd seen the previous ones. The movies were coming out at a reasonable cadence and there was plenty of time to get up to speed. Then they just went off the rails - interconnected continuity even between individual heroes' movies and a crazy fast release schedule meant you were either a superfan or you were lost.

I ended up just watching them at a rate of 1-2 a week leading up to Endgame to get caught up, but it was just way too much.

• 5 films -> Avengers over a 4 year period was reasonable.
• 12 more films -> Infinity War over a 6 year period was much less reasonable.
• 3 more -> Endgame in 1 year was just silly.

Just went and looked it up, and there were another 16 films leading up to Doomsday over 5 years. They're just releasing things faster and faster. Who can (or even wants to) keep up with that?