I recently watched through MCU movies in their entirety again over a few weeks in the build up to re-watching Infinity War.
For the most part the quality is consistently good but there are a few that on re-watching are bordering on slightly better than "bad" and won't watch again in my life.
My least favourite MCU movies
The second half of CA: First Avenger
Iron Man 2 & 3
Ant Man - only saving grace of this was his friend with the funny stories.
Doctor Strange
Thor Ragnarok
Ant Man & Wasp - i literally fell asleep it was so disengaging.
For me Winter Soldier was the absolute peak and while it hasn't gone majorly downhill since then, it certainly hasn't improved.
A lot of this could be superhero fatigue though.
EDIT: On topic, Black Panther is one of the middling MCU movies and absolutely doesn't deserve any rewards recognition.