Literally just finished watching
Maniac (1980). I thought it was really well done. You're kind of forced in Franks world due to the fact that there is no other 'normal' main character to identify with, which for me made it quite creepy. Decent effects by Savini, including a rather excellent self inflicted headshot and a nice gory ending added to the atmosphere.
I am thinking about making it a doulbe bill by watching
Pieces only problem being I have work at 9am