Now, for me a mediocre movie is not a bad one but one that does not stir any emotion in me. And that is worse than a bad movie (for me).
The biggest problem is the weak plot. There are way too many coincidences here that make the world seem very small. The villain is a traditional Disney villain and much like the MCU villains is weak and pose little threat. The main character as is expected from female protagonists these days is perfect at everything - lightsabre duelling, flying and repairing spaceships, wielding the force, etc.
The humour is forced like the directo thought he was doing an Avengers movie. The only one I chuckled at was the thumbs up of BB8.
The characters aren't really fleshed and don't really have an arc. They're best friends within scenes of meeting each other.
The movie also feels like a fan made SW movie with several things being poor copies of the items in the original trilogy.
I dozed off during a few seconds in the middle section. There's nothing really bad or good about the movie.