Not a terrible movie. Not a great movie.
On the plus side, I enjoyed the multiverse aspect. The cameos were cool. The film showed how powerful some of the MCU characters were, especially the villains.
On the negative side, I just wasn't convinced with the villain. Especially the outcome. Also, while Dr. Strange is going through the multiverse, what is the villain doing? Just chilling in their lair taking their sweet time? It was stupid. They could've won. Instead they seem to relish doing... Nothing? The character arc of Dr. Strange isn't hugely satisfying either.
At times the sound mixing is jarringly bad and the use of jump scares are lazy. There's a particular fight scene (think piano and harp...) that is straight up one of the stupidest fight scenes in a marvel movie. Also, some of the close up fights, where the camera is right in people's face, is just poorly done (think Rachel McAdams). I wasn't a huge fan of the directors style.