Mostly the plot and characterization.
The first half was ok, while it's easy to guess what happened.
The 2nd half was just bad, after the truth was revealed, it just became a very Mary Sueish dumb fight. The villains are weak and didn't cause much trouble or feel menacing, it's just Carol smash them. The characterization of the villains are also weak, especially since there are potential for them.
Carol worked with them for a while, but there is no struggle or development between them. Jude Law's character was quite wasted.
Wonder Woman's last fight was a bit weak, but there is struggle, development and the emotional climax. Ares was also not a bland villain, he had his reason.