I must admit to finding Machete a bundle of laughs but the film wears it's irony so proudly on it's chest that it's almost impossible to be offended by it.
Wolf Creek really annoyed me because it was beautifully photographed and the actors were clearly talented but the piece was so pointless and the action boiled down to the same old routine of people (specifically of the female gender) being brutally punished for acting in a bizarrely stupid way. At least your average splatter flick has the language of exploitation to provide a comfort zone for that sort of cinematic rubber necking.
The original version of The Texas Chainsaw Massacre had pathos and almost Beckettesque humour, it was grueling but also demonstrated surprising restraint and provided a cathartic experience.
REC worked on a similar level, it's essentially a zombie film with shaky cam effects but it has layers of scary ideas overlaid onto it as well as some realistic characterisation and it provides a white knuckle coaster ride experience.
House Of 1000 Corpses, started so well, the first act plays like a John Walters comedy and then it became deeply and repellently sadistic.
It wasn't fun in a gooey splatter sense, it had no message or ideas, it didn't even work as a Grand Guignol ghost ride, it was just sick for sick sake.