The goods and bads can be understood better when looked at with specific cases of good and bad occurences of movie-game adaptations.
Spiderman 2, the game, was a fantastically fun game to play. It had a different plot to the movie, with extra villains added in, meaning that it retained some originality, and the web slinging action was just right. It didn’t detract from the film and would have been a good game without the film. Look at the Incredible Hulk games we’ve been seeing recently. Very fun game, doesn’t have any real bearing on the film.
Then you get a game such as the recent Pirates of the Carribean game, or some Shrek games which have been seen. These have simply been thrown together tie ins with no interest in how much fun the games will be to play, but simply how well they will sell. This means that, because of their connections with the movies, young children everywhere really want these games. They whine and moan for them during the run up to Christmas, and the games sell millions of copies.
There we have two sides. You have games which are produced with the movie and are good, with good game designers backing it and trying to make it genuinely ufn and playable. Then you get designers who just want to make money, regardless of whether or not they make a good game.
That’s why I say to always check for independent reviews of such games. The best place to do so, in my opinion, is www.ign.com, as alot of the games on the site have video reviews as well as normal reviews, meaning you can see the game in action before buying them.
Don’t fall for the cons of poor games riding the backs of popular movies. Spend your money intelligently, and vote for good tie ins with your wallets, instead of supporting bad ones because of your children.