Bateman is very funny, the acting of the three leads is good (though the supporting cast doesn't provide a lot of support, and one wants to throttle every child actor who appears in the movie), the funny scenes from the trailer are funny, but not much else works. The directing and camerawork are appalling, two big set-piece action sequences in the middle and end of the movie don't work in the slightest, the writing was mediocre, and someone from the studio really should have done something about the weird and sudden tone-shifts and inconsistent characterization. It doesn't help that the main villain never read the Evil Overlord list. The movie never decides whether it's dark or light, and there's a racial dynamic that's never addressed. Slim complained about weird musical choices, too.
A quick Google search reveals that this was originally written as a very dark movie that got punched up to be more of a kids' movie, but the result kind of gets stuck in the middle without satisfying either goal. The movie is a very hard PG-13, and not appropriate for kids; apparently, the first two cuts were rated R. The seams painfully show where edits were made to satisfy the ratings board, but that really should have been anticipated much sooner and rewritten so the movie isn't standing on the PG-13/R line.
All of this is frustrating, because this easily could have been a much better movie if the script had been a bit more polished and if the director had been less intrusive.