Some of them are poor but a lot of them are good. There are big differences depending on the writers and directors.

The Hulk films are shite.
Iron Man 1&3 are good, 2 is shite.
Thor 1&3 excellent, 2 is shite.
Captain America the First Avenger poor.
Captain America the Winter Soldier sublime.
Guardian of the Galaxy 1&2 excellent.
Ant Man Decent. Any Man and the Wasp superb.
Black Panther 50% great, 50% shite.
Dr Strange, excellent.
Captain Marvel, poor.
Avengers Assemble Ok.
Avengers Age of Ultron Terrible.
Avengers Civil War very good.
Avengers Infinity War magnificent.
Avengers Endgame magnificent.