Graphic novels and manga qualify as media mail ("books"), but smaller comic books do not.

RPG books (Dungeons & Dragons) qualify as media mail ("books"), but boxed RPGs (Dungeons & Dragons) do not (except for book sets.)

Movies (Mortal Kombat, Resident Evil, Silent Hill, etc.) qualify as media mail ("film") while games (Mortal Kombat, Resident Evil, Silent Hill, etc.) do not.

Optical discs of educational software are permitted, but "video games" are not. It isn't clear to me which side educational games fall on.