People here have already mentioned monogatari
I have a serious obsession with this one:
https://www.youtube.com/watch?v=keMAJcNUAsc it's hard to explain why idk
Also, I like the whole "experiment vibe" this one has to it:
https://www.youtube.com/watch?v=keMAJcNUAsc
I also loved the beautifully animated age progression of Ufo Princess Valkyrie (the swimsuit hydra one) and the basic ones from Akihabara Dennou Gummi