I've watched a lot of anime in my 35 years on this Earth. Recently I've been binge-watching series after series. I've seen some ones that I have truly loved, and others that were excellent.
I find this anime different from those. Firstly, the script is astounding. The way it has been translated into English is fantastic, and the depth of the philosophical conversations, and the concepts and trains of thought therein, are highly intellectual. This adds massively to the richness of the characters, in what could otherwise be considered as a kind of swords and sorcery story.
The different characters from history concept made me dubious before they appeared, but they are done in such a unique way and so unexpectedly; that again it adds to the depth of the story. The voices are marvellous in some instances.
This animation is engrossing and fun, with a story that does not feel episodic. I rate it very highly. It's better than Stein's Gate, and on par with Parasyte: The Maxim and Elfen Lied.