1) Hulk with 'Hulk Strength; can punch Thanos and nothing. Mortal Black Widow can kick him and cause him to bleed.
2) Instead of local issues (early Spiderman, Batman villains), everything is about world destruction and/or world conquest.
3) CGI armies are dumb.
I think that they could have focused on smaller stories and still done well. But, they did bring in about $8B and had several good movies, so....
Note: I did like several Marvel films.