Pineapple Express is the story of Dale Denton, a stoner who has a day job in which he "serves" people their court orders and dates a high school student named Angie. Not a bad character basis to start with, I concede. But when he witnesses a murder and goes on the run with his dealer we rapidly descend into the kind of mediocre capering that you'd expect from the likes of Harold and Kumar. Admittedly there are some pretty funny moments thrown in there, like when Saul (Dale's dealer) tries to kick out the windscreen of his car and ends up trying to drive in a high speed chase with his leg sticking through the glass, but on the whole the movie is most disappointing because it refuses to let go and descend into the surreal excesses that stoner movies have wallowed in previously. It lacks the absorbing character analogies of The Big Lebowski, the utter stupidity of Harold and Kumar or the ridiculous absurdity of Dude Where's My Car and consequently might find it hard to please its key demographics.
That said, for a simple piece of entertainment on a rainy afternoon it might not be too painful an experience. Instead of the stoner routes outlines above, the line taken by Pineapple Express is just to produce a solid buddy road movie with a few stoner jokes thrown in there to drag the Rogen regulars back into the cinema seats that, no doubt, are still warm from their last visit. It's lazy and unimaginative, but for a some easy amusement you could do worse.