Mob Psycho 100
This one is still fairly recent, but it's just so good. It's kind of like Dragon Ball Z meets sweet slice of life anime? The Reigen Manga that followed was also amazing!
Revolutionary Girl Utena
This one is straight up a classic and it's been on my list for years, despite knowing relatively little about it. It's notoriously thick and heavy on the symbolism. I can see why it was so popular for its time. I don't know that it's a favorite, but I feel like I'll spend the rest of my life unpacking all of it.
The original Yugioh anime.
I'm cheating a little bit because I finished this one slightly less recently than the others, but also I love it and this thread is making me consider if a rewatch is in order soon. Probably after MP100, because I'm still not over that one.