Finally watched and I can see why this got bad reviews for a few reasons.
1. Anytime you have a super hero thats over powered, it's hard to have any stakes. Which is why Super Man needed kryptonite. it's also why he was barely in BvS and the Justice League. This movie had 3 over powered super heros.
2. It didn't really feel like a movie. Maybe it's because Disney + oversaturated content and overshadowed the movies to the point that this felt like a TV show. It didn't help that 2 of the characters were introduced on Disney +. One extensively.
3. The overall plot was too simplistic and it at the same time a slave to the "multiverse". It seems like everything revolved around setting up the multiverse scene in the after credits. The main plot point was also based on events from the first Captain Marvel. And the plot itself with the supreme intelligence fall out didn't make sense. And to try and tie that into why Captain Marvel stayed away was lazy as hell.
4. You could tell they made a lot of edits. Probably because the script was bad. Brie, Iman and Teyonah did the best the could with what they had to work with but it wasn't much. There was no emotion in this, no real build up. No real stakes. At no point did I feel there was any legit danger.
5. The villain wasn't really a villain based on the plot. She was simply trying to save her planet. And the fact that Captain Marvel had the power to fix it this whole time is
6. The science didn't make any sense either... Hala should've been a frozen wasteland. Everyone should've been dead or indoors or simply became refugees like the Skrulls.
At the end of the day, this was bad writing. Even with the simplistic plot, they could've did more.
Also, Marvel should NEVER introduce a character in a TV series, then turn around and feature them in a movie.
Lastly, I don't understand why this couldn't have been a Captain Marvel solo movie. It seems like that was the original intent, but they decided to shoehorn in the other 2 specifically for the multiverse bullshyt, and it also speaks to how Marvel had no clue of what they wanted to do after End Game.