The SPM series hit a wall with this one. It's the same ol' story: girls have a slumber party, boys crash, creepy things happen, sex is had, driller killer starts killing people, female survivors fight back...but for whatever reason I didn't enjoy this one as much as the previous two. The first one was kinda serious and innocent, the second one was weird and a lot of fun, but this one is boring and cheap-looking. It felt really uninspired.
I'm not sure if the film makers understood what fans of this type of movies really want. We want hot chicks (this is extremely important) in skimpy pajamas, nighties, shorts, whatever doing girlie stuff and partying and getting naked, then some silly boys come over (the stoner dude from Part 2 was hilarious), sexual shenanigans happen (on screen), creepy stuff happens and the killer (who's a total badass like Jason) shows up and massacres the living shit out of everybody. Blood and gore and naked tits everywhere. Unfortunately, in SPM3 all we get is some unattractive 30-year-old looking teenagers acting like dorks until the boring as hell driller killer shows up. He's a total pussy but for whatever reason the other victims literally stand there (for fucking minutes!!!!!!) while the guy eventually kills some people. It's goddamn ridiculous.
My advise: watch Part 1 and 2 and just skip 3. It's not horrible, but a week after you watch it you won't remember a damn thing except that it was boring. Skip it.
I'm kinda surprised that the SPM series didn't go any further than this. The story idea is simple and anybody with even a above average imagination could pump these scripts out on a weekly basis. And as long as you make sure to have really attractive girls, a nice amount of T&A, memorable characters and graphic violence the movie would make money. It seems like a cash cow just waiting to be milked.
Part 1 - The Slumber Part Massacre (1982)
Part 2 - Slumber Party Massacre II (1987)