Horror can do a lot with what it shows, but it can do more with what it doesn't.
A Wizard leans on this.
If you dig the movie Oculus, the fatalistic body-horror of Junji Ito, or other slow-burn dread that escalates into grotesquerie, you may enjoy/be horrified by this.
That said, mind the content warning, check with your group, and have a mechanism to stop the game if it hits anyone too hard.
A Wizard is very effective horror, and unless you're used to consuming horror media with your friends, it can be tricky to gauge how it's going to hit everyone. So, communicate, communicate again, and have a way for people to nope out.
Also probably have a way for people to roll up new characters. A Wizard is *very* murdery, and it might be better in the fiction to be a big group of commoners rather than a small group of wandering blades, so that there's always new adventurers to pull from the mob when someone opens a door and gets insta'd.
This is a very well-made book, from the intense art to the strong writing to the bonus dungeon by Bogleech, but it's probably not one to lead anyone else into blind.
As for the wizard, it's just a wizard.