This film teaches two objects lessons: no number of clever one-liners can carry a film unaided, and a formula that will sustain a half hour TV-show can easily collapse under the weight of a full-length movie.
Yes, the one-liners are often very witty. Yes, the actors deliver them well. In fact, as has been widely commented upon, Hank Azaria's performance as Gargamel is far and away the best thing about this film.
But seriously, that's it.
It has often been claimed that at the core, there are really only a very small number of stories. Stories that we tell and retell over and over again across the generations, with only relatively minor cosmetic changes upon each retelling. Endless variations on a few core themes.
If that's true, then the real job of the storyteller is to disguise this fact. The simple truth is, these storytellers did a lousy job of disguising it. The setbacks, the heartwarming moments, the climactic final battle: all come across as unbearably obvious and clichéd. Everything and everyone we encounter is utterly and completely one-dimensional. I really mean that, by the way. I know it sounds like I'm exaggerating for effect, but unfortunately I'm not.
This is a film with quite literally NO surprises.