Although there are many different genres of film I have chosen to focus on Horror as a wide genre, as this is a personal favorite and I think it is the most realistic due to a small budget. I will narrow the genre of 'horror' down and chose a sub genre for more accuracy.
Horror films go back as far as the onset of films themselves, over a 100 years ago. From our earliest days, we use our vivid imaginations to see ghosts in shadowy shapes, to be emotionally connected to the unknown and to fear things that are improbable. Watching a horror film gives an opening into that scary world, into an outlet for the essence of fear itself, without actually being in danger. Weird as it sounds, there's a very real thrill and fun factor in being scared or watching disturbing, horrific images.
Horror films, when done well and with less reliance on horrifying special effects, can be extremely potent film forms, tapping into our dream states and the horror of the irrational and unknown, and the horror within man himself. (The best horror films only imply or suggest the horror in subtle ways, rather than blatantly displaying it, i.e., Val Lewton's horror films.) In horror films, the irrational forces of chaos or horror invariably need to be defeated, and often these films end with a return to normalcy and victory over the monstrous.
Of necessity, the earliest horror films were Gothic in style - meaning that they were usually set in spooky old mansions, castles, or fog-shrouded, dark and shadowy locales. Their main characters have included "unknown," human, supernatural or grotesque creatures, ranging from vampires, demented madmen, devils, unfriendly ghosts, monsters, mad scientists, "Frankensteins," dualities (good against evil), demons, zombies, evil spirits, arch fiends, Satanic villains, the "possessed," werewolves and freaks to even the unseen, diabolical presence of evil.
All of this text was copied from http://www.filmsite.org/horrorfilms.html