As for the other films, most of them are by this Friedberg/Seltzer team that appears to be churning out assembly line spoofs rather than taking the time to craft a good one. I learned something as a video clerk - spoof movies, just like sci-fi/horror and "blue" movies, no matter how bad will almost always see a return for years to come. That's why studios don't seem to waste time making them good. They really don't have to.
Hey... I'm just saying Mad Magazine has been churning out satirical film parody articles since the 1950's, and with recent exceptions, they've all been gold.
I think the main problem is they started by parodying a genre, and somehow they felt that they need to parody every single movie that came out that year. This year, the movies didn't even come out. They made fun of them SOLEY on the trailer (Something Cracked Magazine did in spades). They feel they need to make a reference to everything, and make them cheap jokes at that.
If they, however, made fun of one MAIN movie and added in elements of others sparingly, they'd have something. Even Robin Hood Men in Tights was a higher quality parody for that reason. They made fun of one film, and parodied the conventions and cliches of the film itself.