I think the deal with this movie is that it has about 2 minutes of really, really funny moments and it makes a very good trailer and a lot of people came in with expectations from the trailer and this time the movie doesn't live up to the trailer. It's a little more sluggish and drags a little slowly for such an exciting premise, and i think i'm seeing from the comments people having a love/hate relationship with this movie.
However, if you look at this movie for what it is and not what it could have been considering the talent of the cast, i think it's still pretty good. Julia Stiles is clearly the star, she's so giddy and carefree that set among the conformity of everyone else, she just glows and the whole audience falls in love with her along with Lee. The rest of the cast, of course, Lee's testosterone-filled coworkers, his elegant mother-in-law, his fratlike friend Jim and his bride-to-be all do an excellent job of fitting into stereotypes of conformity and boringness that make Stiles stand out in the first place.
Lee doesn't live up to his costars, i don't think, but you could view that as more that they're hard to live up to. Maybe that's one source of disappointment.
The movie itself, despite a bit of slowness and a few jokes that don't come off as funny as the writer's intended, is still pretty funny and I found a rather intelligent film. The themes of conformity and "taking the safe route" seemed to cleverly align on several layers. For example, there was the whole motif of how he would imagine scenarios but would never act on them until the last scene, or how he was listening to a radio program on the highway talking about how everyone conforms, or just how everything selma blair and julia stiles' characters said and did was echoed by those themes of one person being the safe choice and one being the risky choice.
The other good thing about the movie was that it was kind of a screwball comedy in which Jason Lee has to keep lying his way through the movie and who through dumb luck (example: the pharmacy guy turning out to be a good chef) and some cleverness on his part gets away with it for the most part.
While it wasn't as funny as i expected and there was a little bit of squandered talent, but overall it's still a good movie.

I don't normally feel much of an incentive to comment on films I don't like, but in a case like this one, I just have to say something. This movie is terrible, illogical, and stupid. There are so many flaws in the storytelling that I don't even feel obliged to elaborate on because it's time for me to move on from this experience. The most annoying point is, however, that at no point in the film does anyone explain whether the motivations for Bacon's character's madness are due to a power trip or a physiological reaction to his condition.
Granted the special effects are impressive, and in the past Paul Verhoeven has done some good stuff (the director's cut of Robocop on DVD is great). However, this movie is stupid and generally doesn't come near to explaining the point or technical aspect of the subject matter, and instead settles for predictable action without any enjoyment.
In short, as many other reviews here say (wish I had read them before...) - Stay away from this film!