Portman really bugged me (and lots of people) in the Star Wars prequels--especially Episode II. I can't describe exactly what it was, something like a mix of stiff, understated, reserved, and breathy.

I got the same thing from Brie Larson in Captain Marvel. She just wasn't firing on all cylinders. She was trying to be funny, trying to be cute, or trying to be tough instead of just being those things.

Decent movie but Larson could have been better, or perhaps the role could have been better cast.

I still think Thor 2 is the worst Marvel film, but this one is in my bottom 3 after the first watch.
EDIT: persuaded by subsequent posts, I'd put it in my bottom 5 ahead of Ultron, IM2, and Thor 2, and behind GG2. I just think each time I watch Brie Larson underachieve, I'll be more bugged and less likely to watch it again. To each his own, though.