Britta's Tacos was good. The lesbian/bi Jackie stuff felt dumb (they could've done it better with someone more prominent like Tom, if he'd broken up with Star sooner), but not in a way that hurt it, if that makes sense. I can look at that decision and just SEE the crew planning it out for progressive points/to retroactively make Jarco worse, but within the episode it's presented naturally enough.
The portal to the Realm of Magic being in Britta's Tacos was clever. Either that was planned out as far back as Battle for Mewni, or someone actually looked at how Ludo's bird and spider somehow made it back to him after being stranded on Earth and came up with an actual solution. Either way, it's a level of thought and connecting earlier details that you don't see much of in S4.
Mewmans being humans (or more like humans that mutated slightly from the magic over centuries) was completely fine. Unpopular opinion, but they'd already made them way too obviously similar to humans to really buy that they were something else that just evolved differently, and Mewberty/Butterfly form was also already way too obviously linked to magic to be something every Mewman could do. It made sense (although it does feel shitty that they could've tied that into the monster rights shit somehow, the main couple being different species, but clearly they had to step aside for Eclipsa and Globgor's revolutionary vagina and cock).
It wasn't really done well, but I like Mina being the surprise final villain, or maybe antagonistic force since there was never a real final showdown. The plot demanded a Mewman villain and I like the idea of a character who showed up in what seemed like a filler episode being revealed to be legitimately dangerous. I also liked the slight depth she got and I'm glad she lived. By the end she might've been the last character I gave a fuck about.
Ending the series with destroying magic and the monarchy was good and took balls.
everything else suuuuuuuuucked