I'll just say this, of the three shows that ended….they all got pretty bad (I'm in the minority about not caring for the last few seasons of SU) near the end. But boy oh boy, with Adventure Time and Steven Universe the shows just went from great to "Meh, kinda disappointing" while Star Vs went from Great to "Holy shit that's Danny Phantom Season 3 bad." Like Star Vs just hit a fucking brick wall.

Without going into too many spoilers, Season 3 was when it started to get interesting, as it started focusing more on uncovering what was wrong with Mewni. Some teen romance drama happened, but was tolerable. Then the ending happened, which involved a metric fsckton of unanswered questions, a few characters going off the rails of characterization in order to push the plot, and a touch of genocide as well.