What a wild ride. I came into this one hot on the heels of School Live! based on a recommendation, and hot damn do they both know how to gut your emotions like a fish.
Story - Honestly the weakest point of this one. There's some confusing plot developments and probable holes that make it really hard to make sense of the world at large. But honestly the main plot of the story isn't really the reason you'll keep watching anyway. More to the point - take your bog-standard High School Life anime, mix it up with some Rebels-Fighting-With-Guns, and add a dash of Afterlife/Isekai, and you'll have a good idea of what to expect.
Animation - High quality. Nothing *too* fancy, but definitely more than what I expected. Everything is detailed appropriately and movements are smooth in both action and non-action scenes.
Sound - The pinnacle of this work. Amazing orchestral pieces, high quality voice acting, and believable effects/background noises. I'm going to look up the soundtrack to this thing and listen to it on the side, just because it's so beautiful. Don't you dare skip the OP.
Characters - Surprisingly robust and believeable compared to the main story arc, and in the best way. Where normally a lackluster story is accompanied by lackluster character design, this went the complete opposite direction, and the narrative rides on the backs of these very expressive and detailed characters. Everyone has a unique personality and motivations that really drive themselves forward as a unique and interesting person. The relationships these characters build with each other, and their reactions to the realizations they make, are far more compelling than the actual story.