Dark Horizons (thanks Ant) has a translated summary of a story form a Czech reporter who visited the DOOM movie set in Prague. The report outlines various aspects of how the movie's story will diverge from the game's. Here's a bit:

The story follows eight marines, teleported into a command centre of a secret base on a remote planet. There, they learn that something strange is happening and soon monsters start to appear. The monsters aren't from hell, but rather people mutated by some nasty super-virus although the monsters look very similar to those in the game.

...Producers claim that the film will be more of a horror than an action shooter.

There will be loads of shooting though, especially in the end where a large number of sequences will be shot purely in "first-person" perspective of the leading character (Karl Urban). The chainsaw and Bio Force Gun do appear in the film.