Instead of just spoofing stuff it tries to add "serious" elements - Pegg's relationship with his girlfriend in SOTD, Frost's relationship with his dad in HF. A lot of the comedy is undercut by over-directing. Quick cuts are not conducive to comedy - somebody needs to sit Edgar Wright in front of some John Carpenter films and teach him about static wide shots. It works in a half-hour Spaced episode but needs to be varied a bit in a 2 hour film.
There is too much in-jokiness - Pegg seems to think SOTD was some kind of masterpiece that needs to be referenced, so endless repetitions of "cornetto" and "need anything from the shop" and "go to the pub" are served up. Yawn. Frost repeats his dull "slacker " performance, with poor acting, from SOTD. He even tries to do serious "emoting", with embarrassing results. HF is not the kind of film that needs a "serious core" so why try to give it one? Just do lots of stupid gags.
Some nice cameos though - Edward Woodward, Timothy Dalton etc. The middle segment of the film is a slasher spoof and probably the most effective part as there is an actual sense of mystery and danger to distract you from the iffiness of the comedy. And some of the gunfight finale is almost Robert Rodriguez standard (but nowhere near John Woo standard). But in the end it doesnt disguise the feeling that this is over-long, over-indulgent, and worst of all, not funny enough.