Not so long ago, when a movie was completed and released for the public to watch, there was a very simple pattern to things. The movie was scripted, then edited, then recorded and directed, then cut and shown to a test audience, then tidied up and released to a waiting public. Now, pretty much no blockbuster movie is complete without a tie-in video game. Well, some are, of course. An 1800s costume drama where all of the action is in what is said (and left unsaid) will not work particularly well in a gaming context. Every action movie, however, requires its own video game.
In truth, a good movie does not necessarily make for a good game. You can like the character and appreciate the storyline, but for a video game to work it needs to have a real sense of interaction between what the gamer does and the eventual climax. Movie merchandisers do realize that someone might enjoy a game so much that they will go and see the movie or buy it on DVD, so the better software houses do tend to get the contracts to make the tie-in games these days.
One thing that is commonly recognized by gamers, however, is the fact that quite often a movie tie-in video game is very heavily based on an existing game, but with the familiar characters, settings and storyline all but superimposed onto the game. Selling to a gaming audience is not the same as selling to movie fans, and this is a risky stratagem. The best movie tie-ins remain those which are developed synergistically at the same time as the movie is being made.