The first movie is very good, part of the reason for that is they kept the scope relatively small. They introduced a handful of characters, established the concept of mortal kombat and did so in a way that makes it a good stand alone movie, you dont need to be a long standing fan of mortal kombat to enjoy it.
This sequel though they tried to do too much too fast.
They introduced lots of characters, some of whom get no lines of dialogue and are never addressed by name so anyone not already familiar with the franchise wont understand the relavence of them or their abilities.
Not only that but the characters that did get dialogue and played roles in the story were very shallow, I will avoid spoilers here, but there were multiple new enemies introduced, each with their own goals and methods and since the movie tries to squeeze 3 seperate plots into just 80 minutes of screen time none of them got the attention they deserved so all of them fall flat.
Lastly the ending felt very very rushed, this point ties into the one above about squeezing multiple stories into 1 short movie and this is most apparent towards the end. The writers simply copied the whole DBZ super saiyan, instant miraculous power increasing transformation mechanic which culminates to a dissapointing, unsatisfying, lazy and to be frank idiotic final few sequences that are utterly ridiculous and very very far removed from the entire concept of mortal kombat.