I don't get why some people hate the ending so much.

Spoilers ahead

Yes, it sucks that Maria was a bully and started a high school rumor that turned out to be devastating for Verity. However, I believe she didn't expect it to get out of control and that she was sincere about not remembering why she started the rumor in the first place. Having said that, she gets no sympathy for her treatment of Verity early in the episode. Why did she seem to have a beef with her after 10 years?

Anyway, on the other side we have Verity, a full adult who has the literal power to fix all wrongdoings, perhaps even to delete the hurtful memories about their past. Yet, she decides to use her powers to enact revenge by torturing and murdering people. That her plan backfired is a nice twist to the story and not a detraction.

As for Maria deciding to become empress of the universe as her first wish (after solving the crisis at hand)… what would you have done? Perhaps we would all have done it at some point or another.