Iconic for 70's horror manga. Being only 42 chapters this is something you can read in a day or two, and I recommend that you do. Drifting Classroom does/creates some genre staples while not being overly confusing. The themes are obvious as man fights itself, nature, starvation, loneliness. You see children grow up and go through a lot in this manga. The horror comes from a bit of body gore, a bit of psychological dread, some terrifying monsters, and ultimately being taken from home against their will. Before reading I saw on reddit people not liking the ending of this one, however it all added upin the end. Mostly everything was addressed and wrapped up nicely to be conclusive.

Give it a go