There seems little point in having this film be computer-animated in fact, the script, by Dan Harmon and Rob Schrab (both best known for the famously never-aired Owen Wilson/Jack Black TV pilot Heat Vision & Jack), was written with a live-action adaptation in mind. It was later thought that a final transformation in the movie's third act would be far too ambitious for the realistic approach, but honestly, what we see isn't that different from stuff that has previously been achieved via stop-motion animation. Even the advantages granted by the digital format aren't fully utilized; clarity is usually one big plus, but first-time director Gil Kenan often deliberately sets the background out of focus, or shifts the focus as one would in live action, when it's completely unnecessary to do so (The Lion King was guilty of similar tricks in 2-D, and neither movie is well served by the technique, especially with more and more of us accustomed to HDTV).
The plot isn't much. Youngsters DJ (voiced by Mitchel Musso), "Chowder" (Sam Lerner), and Jenny (Spencer Locke) are intimidated by a creepy old man named Nebbercracker (Steve Buscemi, animated in such a way that one can easily imagine how well he might have played Gollum) and his frightening old house, which seems to consume toys carelessly left on its lawn. When Nebbercracker apparently has a heart attack, the house gets even scarier, acting autonomously and making scary "faces" with its windows, door, and porch. Eventually the kids go inside, more or less copying the climax of every Harry Potter movie, in which the hero, the heroine, and their goofy friend go down into that scary room no one has ever entered and face supernatural trials. The coolest thing about Monster House is that Kathleen Turner's face was actually motion-captured to create the house's expressions, creating perhaps the most wooden performance of all time.
Motion-capturing Turner is one reason to use computers; another is the ease with which a CG cartoon can be translated to 3-D. Some theaters will get Monster House in this format, but no particular effort was made to present it that way for critics. It seems an odd call, but Disney similarly held back the 3-D version of Chicken Little, and Warner Bros. did likewise with the 3-D IMAX version of Superman Returns. If the filmmakers' fear is that critics tend to dislike special effects, they should recall that most of those who saw The Polar Express in 3-D IMAX two years ago came away with a far more favorable impression than they got from the 2-D version. The novelty of the experience, and the potential richness of digital 3-D, can overwhelm minor quibbles, and it's easy to see how Monster House might work better that way.
As with Over the Hedge, there's a sense here that computer animation may be getting too realistic for stories that are meant to work as cartoons. Why make the backgrounds look so real if the characters are going to be brazenly cartoony? And if you're going for cartoon characters, why give them such grungy textures? The kids and parents on display here look like Jimmy Neutron bit players who've been rolled in dirt. (And hearing Jason Lee's voice emanate from a teenager is just plain weird.)
In fairness, though, the children at the press screening seemed to enjoy things far more than the adults. An unpleasant gag about peeing into Mountain Dew bottles elicited uncontrollable laughter, as did one about an adult diaper. They also loved Nick Cannon's cameo as the token goofy black guy. For this adult, however, actual human beings on-screen might have ratcheted up the tension, of which there is none. It's no coincidence that Nebbercracker is the most interesting character: He's the only one who looks like the actor voicing him. None of this is likely to bother the kids, but unless your theater shows Monster House in 3-D, try sneaking into the next room while the young'uns are preoccupied.