Unbiased review:
The story is easily amongst the best I've ever read. Contrary to what I've seen a minor portion of the more casual readers think, the basement reveal is very well thought out & not an asspull, given the blazing trail of hints showered throughout the buildup to the reveal. Even past the basement arc, the story keeps building up tension & intrigue, despite most major reveals are already unveiled. Given this, it is evident the author seems to have a very good idea of the direction & conclusion of the story. The story is not flawless however; there do seem to be a few number of minor plotholes and questionable character decisions. On the other hand, readers wishing for a more apocalyptic world will be eventually disillusioned with the direction of the story. 10/10

Art: The art is unquestionably awful in the beginning few volumes, but gradually improves. My recommendation is two watch the first 2 seasons of the anime given that the source material is a bit of an eyesore. However, the author's drawing improves exponentially, and reading from chapter 50 is a smooth ride. 8/10

Character: Character development is stagnant in the first season and the corresponding source material. Characters having major roles in the story have no real development until their reveals, after which they are sidelined again. Character development slowly picks up from Chapter 50, albeit for select characters. Characters are on two extremes; either extremely well fleshed out or unknown.
Character development is a highlight of the latest arc, where almost all major characters have some personality shift. 8/10

Enjoyment: Depends on you're drawn to. If its the story, 10/10.
Characters, will vary (although start negatively).
Personally I thoroughly enjoy it.

Overall: 9/10