I was just thinking, can I honestly think of a perfect anime? But yes, Steins;Gate, without a doubt. It is so perfect that the second season, which is an almost-perfect anime and fits neatly in the events of the first, can only bring it down in perfection.
I recently rewatched it and there’s a lot of foreshadowing and plot points that hit harder when you see them coming.
My only complaint about Frieren is the exam arc. Up till that point, it’s a tightly knit group of adventurers traveling with a very vague goal, it’s about their journey and their internal relationships. But the exam arc has an actual goal and introduces a lot of recurring characters, which really changes the vibe of the world. I liked it enough in the end, but I would’ve preferred more smaller arcs. On the other hand, season 2 could put the exam arc in a whole new light and make me appreciate all those characters much more when we see them again.