I actually think a Dead Space movie would be scarier than the actual game. The concept behind Dead Space is terrifying. An alien life form that drives you insane, then brings back the dead in mounds of walking flesh in order to make more of itself. And remember, there is no defense against this thing. If, or rather when, you get infected, that's it. Unless you manage to get away, and even then you're not safe.
There will need to be more characters, because if it just starts out with Isaac, we know that he can't die so there will be no suspense in the movie. We can't get a clear look at the Necromorphes for at least half of the movie, but we will need to see their handy work and hear them. Not sure if including the babies is a good idea though. And please, for the love of movie making, NO SHAKING CAMERA WHILE RUNNING. I'm so tired of movie cameras trying to portray the panic and chaos of what's happening simply by acting like someone is running with the camera. No no no no.