I honestly think this is better that Frieren in some ways. The beginning of Freiren explored this whole theme of time passing by differently for you than everyone else, and watching everyone grow old around you. And in the beginning it did that really well, going into themes of legacy, memories and parting ways. It was interesting exploring that from Frieren's perspective.
However later on, more and more it turned to pretty much just your regular (albiet well made) adventure manga.
THIS manga however, seems to never stop with these themes. Sure we got the adventure as well, but it never lets up on the non-aging aspect, which I find super interesting. I can't really come to think of any other manga that did it quite like this. To Your Eternity somewhat deals with non-aging, but at the same time that isn't really the focus of it
Anyway, good manga, ty tl