This movie might've worked if...
...there'd been some kind of hero with whom to identify. Every movie, even a comedy, needs someone to whom the audience can relate.
When I first saw this movie, I assumed Andy Comeau would be playing that role. Like any hero, we follow him almost from the beginning and we're told about a goal he has: impressing his fiancée's parents. But this goal gets dropped early on to make room for all the headless shenanigans, and even then Comeau's character doesn't do much except react to what the other characters are doing.
As it turns out, Joe Pesci is the actor who comes the closest to being a hero. He has a definite goal (don't disappoint his bosses and get killed), we follow his point of view quite often, and he actually takes action throughout the entire movie. Problem is, he is so unlikeable that he can't be called a hero by any stretch of the imagination.
No matter how wild a movie gets, there has to be at least one character who is both relatable and interesting, whether it's George Clooney's in FROM DUSK 'TIL DAWN or Leonardo DiCaprio's in GANGS OF NEW YORK. 8 HEADS IN A DUFFEL BAG had no such person.