Looking at the positive comment, I assume this is good? But why is the rating only 9.0?

usually when a story’s rating has a 9.0 or 8.9 its probably not that good but not horrible, either boring or just stupid with the same cliche plot.

It's alright. There's couple interesting things about it, some being unique, but the series also isn't something I'm desperately waiting updates on (unlike some other series on this site). The writing, in terms of the comic (I can't remember if this was an original or an adaptation from a novel) can feel a bit awkward at times, or not done the best way (things like pacing and dialogue). So, like the person above me says, it's not amazing but it isn't downright bad either.