One big complaint I have of Avengers / Marvel is the lack of any particularly memorable orchestral themes. Lots of other movies series have done this over the years, and even more recently - you can hum the Pirates theme, or maybe even Wonder Woman's (not all that hummable, but memorable), but the Avengers music is so sort of blah that even though you recognize it when you see it, you couldn't recall it to your friend. It's sort of a problem that plagues a lot of modern movies though - the style is more propulsive that melodic.
John Williams true genius was his ability to take 2 bars of music and make it so catchy that you can recall it from memory. Sing along with me....
Indiana Jones!
Star Wars!
Superman!
Jurassic Park!
Jaws!
Harry Potter!
Now- Avengers!
You get my point...