This is a review of the anime only. I have not read the manga.
This is an anime that you really have to pay solid attention to while watching. You can't miss even a few seconds without suddenly being lost. I like that it moves fast and is complex like that but it makes it exhausting to watch, especially if you're trying to marathon it, the way I did.
The first thing that jumped out at me about this anime was the art style. It's phenomenal. It's very different from what we're used to but it's still absolutely stunning. I usually despise Western cartoon art styles but this was done spectacularly well. I loved it. It was sort of shoujo-esque in that there was a lot of focus on the eyes and lighting but I liked that.
The story was really confusing to me but I wasn't able to devote 100% of my focus and I got tired of rewinding every few minutes. There's a lot going on in the fore and background--a lot of players, a lot of plotlines. I don't know how they could have done it differently without it getting boring so honestly, it's just one of those that requires your full attention. Know that going in and you'll probably fare better than I did.
My one real complaint was that there were so many characters that I never really got attached to any of them. I liked a lot of them but not as much as I could have. I really would have liked to have had more depth with James, more backstory. I also would have liked him to be a little less immortal. This show suffered from Stormtrooper syndrome in the worst way. Hundreds of rounds of bullets flying around and James doesn't get hit by a single one. It got to be ridiculous.