People who saw "Dude, Where's My Car?" either loved it or hated it. What you thought of it probably depended on your impression of the movie beforehand. If you're a fan of "Cheech and Chong"-style stoner movies, and you're a gen-xer or younger, you probably enjoyed it. If you knew it was going to be stupid and expected little, you probably didn't like it.
I thought it was an excellent movie. I know not many serious people felt that way, but there you go. I like a movie that is self-consciously stupid, and I felt that this one pushed that concept to the limits. Everything seemed to be done to give the impression to the uninitiated that this was a bad movie. The writing on the surface seems terrible; the acting on the surface seems terrible. And I'm not going to say you have to look deep to find meaning. The deeper you look, the less meaningful the movie becomes.
The filmmakers are working from a long tradition here. Give Ashton Kutcher and Sean William Scott some credit; they are both gifted comic actors, and they are both funny here. The movie doesn't make much sense, even when we find out what the continuum transfunctioner is. The bare-bones plot seems like nothing but an excuse to have these two half-wits go on a series of misadventures. And yet, I don't think it can be denied that these vignettes are funny, often hilarious. And the dialogue is so stupid that it's really hilarious as well. Consider:
CHESTER: Dude, you just touched Christy Boner's hoo-hoo. JESSE: Shibby!
MR PIZZACOLI: A trained dolphin could deliver pizza better than you too. JESSE: But then the pizzas would get all wet!
And so on. The movie is full of non sequiturs and dumb dialogue. And if you're in the right frame of mind (and no, I don't mean high) then much of this is hilarious. The fight with the Chinese food takeout lady ("And then?" "No and then!" "And then?" "I refuse to play your Chinese food mind games!"); the guy in the cage (played memorably by Andy Dick); the transsexual stripper (or, as he/she puts it, "gender-challenged male"); the race of identical hot chicks, and their enemies, the "totally gay Nordic dudes"; the cult of Zoltan; and, of course, the continuum transfuctioner itself, which is a Rubiks cube that Chester is able to solve, despite barely having the brainpower to tie his own shoes. This is all very funny, and I think you have to be some kind of film snob to not see the artistry that went into making a movie so stupid that ends up being so entertaining.
What you have is the most likely future cult classic to come out in many a year. It's a stoner movie where nobody (human) does any drugs; a mystery with no real mystery; and a dumb movie that, because of the calculatedness of its lunacy, is not really so dumb after all.