After reading a bunch of negative reviews from film critics, I assumed that I too would be disappointed by the movie, but I thought it was thoroughly enjoyable! For starters, its running time is much shorter than that of most blockbuster movies these days, so that was a huge plus. I also thought it was refreshing to see three women leads in a superhero movie for once, with two of them being women of color (though I suspect that this might've been one of the reasons why the movie got panned by so many people).
And despite what many reviews have said, I didn't find the plot hard at all to follow. I think the only Marvel movie/show you needed to have watched before this one would be Captain Marvel, and it would probably help to at least have heard of Ms. Marvel/Kamala Khan (I have yet to watch that series, but I'd read some articles about the show when it first came out so was at least somewhat familiar with the character). But even if you haven't seen Captain Marvel, I think you'd be fine (I'd seen both Captain Marvel and WandaVision, but I could barely remember what happened in either of those, and yet I was still able to grasp what was happening in The Marvels without any issues).
I thought the film included just the right amount of humor (without going overboard), and the swapping concept was cool and well done. The post-credits scene is also one of the most epic ones you'll ever see in a Marvel film.
My only major complaint is that they really didn't seem to know what to do with Park Seo-joon, the Korean A-list actor who plays Prince Yan. It's like they just threw him in there because they knew his fans would watch the movie simply because of him. I wish they hadn't forced him to say his lines in English, b/c his English pronunciation is worse than that of most Korean actors (besides, the whole movie takes place in space and in a fictional Marvel universe, so why do all the characters have to speak English anyway? Having Park just say his few lines in Korean would've been so much better, both for him and for the audience.). And don't get me started on his hair and makeup--they really should've hired stylists who work on K-drama sets because I've never seen Park with such awful hair and makeup.
But despite the fact that Hollywood still hasn't figured out how to properly cast and portray Korean actors in their films, I thought this movie was still worth a watch!