They wiped away our interesting main antagonist that's been built up for three seasons in an anti-climatic way that didn't really explore his character at all or even make much sense, all so they could focus on Eclipsa.
It feels like Meteora was tacked on for some conflict and she had potential after she attacked St. Olga, but than they fucked her design/personality/abilities. She was overall fine and her last confrontation with Star/Eclipsa was well done, though would've preferred if she stayed dead.
They spent like a dozen episodes going on and on about how Star has feelings for Marco but than wham she dates Tom and I just can't make sense of what Star is thinking. Most episodes were really boring but that's sort of par for the course with Starvs. S3 never got close to being as good as peak S2. Best thing about the season for me was the Realm of Magic, really neat concept.
They've done an alright job developing Star's character over the series, but Marco is a dud. Princess Turdina pretty much ruined the fanbase. It feels like a better show would've ran with the Running With Scissors concept for him but instead it was completely dropped after the episode. We're all hoping his inevitable Monster Arm thing will be good.
That episode was awesome and gave us a lot of perspective on the world.