Never Sleep Again and Crystal Lake Memories are great documentaries.

If you have not seen these documentaries, then I recommend that you check them out. IMO, they are better than the actual movies they're documenting.

They're a very in depth look at both the Nightmare on Elm Street and Friday the 13th series' which include many interviews with actors, producers, directors, special effects artist, etc. They do a great job at explaining in detail what kind of affect these series' had on pop culture and the horror genre. There's also a lot of behind the scenes info from each one of the movies in the series'. They're long, but they are great.

They're on SHUDDER.com. You can get a free 7 day trial. Worth checking out.