Well, i don't know if it's a bad movie or not.
If you ask my 6 years old nephews, they didn't like it because it was complicated and not too really funny.
I agree with them: the part about the prophecy isn't really clear and Chabat is boring when he tries to make laugh with private jokes (here, Celine Dion). In addition, there's too much useless characters thus too much thin stories. For example, Geraldine is maybe sweet but her character is transparent here. In fact, it's too scripted for a comedy.
On the other hand, Chabat is a great actor and his portraying of this goofy reporter is fun. Debouze, Wilson are boring as usual but they are watchable as they stand for punching bag. Fred is excellent as a pseudo dictator and proves another time that he can play anyone.
As for Marsu, the movie decides to film it in his native jungle. It's faithful to the comics and it's exotic.
In conclusion, maybe it's a disappointment for those who waited a crazy frenzy as "Gremlins" but it's not a wasted time also.