Maniac

It's a showcase for sweaty character actor Joe Spinell, who appeared in a lot of major films (The Godfather Part II, Taxi Driver) in small roles, and larger roles in more dubious fare (Starcrash). The story was inspired by the Son of Sam killings, with Spinell as the ranting, depraved killer. The film was notorious for its (at the time) very graphic killings, featuring the work of make up FX legend Tom Savini.

The movie's appeal will be limited, but if one enjoys that particular brand of late-70's/early-80's NYC grime and sleaze, it's a must-see. Director William Lustig made several other genre films (Vigilante, Maniac Cop) before starting the Blue Underground home video company, who are the prime source for Italian genre films on disc (horror, giallo, spaghetti westerns, crime thrillers, etc.).