Well not all of them are bad. I played LOTR The Battle for Middle Earth strategy game for a long time. It was also fun to play in multiplayer. But I must agree that in general they suck. There are a lot of examples of bad movie based games, but I can't recall of any particular title now.
i played this one star wars game for the ps1 and it was ok until the swamp level you were trapped and people(robots) were shooting at you EVERYWHERE you couldnt get out it was ok though 7/10
I could go back and forth on this... there are some movies that had great video games (i.e. look at the Star Wars games.) but there have been terrible videogames that came from movies...
some videogame based movies aren't to bad. i liked doom and final fnatasy the spirits within. the problem is, there aren't that many of them, so the really great film makers aren't involved in these low budget and cheap wastes of time and money (i mean video game based movies). however, i heard that peter jackson, the director of lord of the rings os making the halo movie. all three of the lord of the rings were really good, so something as epic as halo should be just as good if not better. you just need the right people doing movies on the right games.