19. Parasyte -The Maxim-
At first, Parasyte -The Maxim- feels a little too much like a generic shnen anime, as a young student's arm is taken over by a sentient parasite who reveals that similar parasites have taken over the brains of seemingly ordinary people.
Parasyte is, of course, similar to shnen in a great many respects (and there are some excellent purely shnen ahime out there, as we will see) but the sophisticated philosophical musings on the nature of identity and the strong character development (which includes dealing with alcoholism among its themes) makes it more in the vein of seinen, aimed at a more mature audience.
That said, there's plenty of excitement and spectacle here for fans of action anime, and some of the transformation sequences are clearly inspired by great body horror movies, particularly John Carpenter's The Thing.