Some may look at this film as either a low, bottom of the barrel joke to make fun of conjoined twins or some will be expecting a laugh a minute no brainer movie. But anyone who knows what a Farrelly movie is like (and that means MOST of their movies) that this one is neither. Many people fail to see the heart and message that most of the Farrelly bros. films offer. It isn't about gags or over the top humour; they are really about the underdogs. The ones who are trying to fight their way to some degree of respect in whatever they're trying to achieve. Yes, there is some humility in it, but overall, these characters do learn a lesson as well as the people around, against and for them. If you watch other Farrelly bros. films you can see a trend here.
"Kingpin," for instance, takes the man who use to be the"could have been" pro bowler of a small town. In an unfortunate circumstance, he loses his hand and therefore his dreams of becoming a pro bowler have drowned any possibilities of it ever happening.
"Dumb & Dumber" seems to have you rooting for the underdog wackiness of the two friends who seem to not get it together with thier intelligence, but they still earn the respect from others because of their overall goodheartedness. Let's say they're kinda like Lennie & George in "Of Mice and Men." Just a slight bit less brighter.
If one can overlook the overall silliness and see the message behind these movies, then one can truly and successfully dissect and analyze a story, with an open and humble mind.