While there are some “hard number” metrics to cite when it comes to how a movie is received, Rotten Tomatoes, Metacritic, IMDB, there’s one that gets circled back to more than others when it comes to audience reception: Cinemascore.
This usually measures what’s a “crowd pleaser,” skewing higher in terms of blockbusters a lot of the time as it tries to measure audience satisfaction. Now, Captain America has the lowest Cinemascore in MCU history, a B-, which may not sound that bad, but in context, it definitely is, especially when you see the overall chart. That would be:
edit: the list is missing some entries and has the ratings wrong for others, so I've redone it.
A+
The Avengers
Avengers: Endgame
Black Panther
Spider-Man: No Way Home
A
Ant-Man
The Avengers: Age of Ultron
Avengers: Infinity War
Black Panther: Wakanda Forever
Captain America: Civil War
Captain America: The Winter Soldier
Captain Marvel
Deadpool & Wolverine
Doctor Strange
Guardians of the Galaxy
Guardians of the Galaxy Vol. 2
Guardians of the Galaxy Vol. 3
Iron Man
Iron Man 2
Iron Man 3
Shang-Chi and the Legend of the Ten Rings
Spider-Man: Far From Home
Spider-Man: Homecoming
Thor: Ragnarok
A-
Ant-Man and the Wasp
Black Widow
Captain America: The First Avenger
The Incredible Hulk
Thor: The Dark World
B+
Doctor Strange in the Multiverse of Madness
Thor
Thor: Love and Thunder
B
Ant-Man and the Wasp: Quantumania
Eternals
The Marvels
B-
Captain America: Brave New World
...
Initial box office receipts are pretty good, and better than other low-scored MCU movies, but this still has to be somewhat alarming for Marvel to have a movie received this poorly. As it stands, this is the third lowest scored film on Rotten Tomatoes, the lowest scored film on Metacritic and the lowest scored on Cinemascore now.