@Phantom..."story"? The Doom video game series is hardly
War and Peace. If it wasn't for the "hell" angle it would just be a rip of James Cameron's
Aliens. The movie is a rip because the video game's story is a rip. It's pretty hard to pretend otherwise and try and eck out some kind of dramatic tension. Action movies are about action, if you get a good story, that's just a bonus, and the
Doom series and it's movie are, IMO, about the same thing.
As for changing the story, I assume you're referring to the "hell" elements. while the "hell" aspects of the video game are not something that video gamers necessarily concern themselves about - although we should note that many ToJers didn't pick the game up for that very reason - for movie goers, it's a different thing. If they made this movie with the same "hell" elements as the video game, the movie would quickly be lumped the horror genre and makes it less appealing to the masses as a whole. The movie makers don't want their movie to be picketed by protestors. Aliens are more palatable than fire slinging hell spawn.
I'll leave Serenity comparisons and comments alone, there's obviously some fans here.

But to suggest that Doom has more mass appeal than Firefly is pushing it.
The Rock, however, is a different story. It's a sci-fi-action film with The Rock in it, that's why people (the masses, non-gamers) are going to see the movie, not because it's Doom.
Ditto Tomb Raider. If that film didn't have Angelina Jolie in it and just some no-name or B-movie actress, would it have made any money? And it's not like they marketed Tomb Raider or Doom by accentuating the source material as a selling point. I'd be suprised if the majority of people out there who have heard of the film know that it's actually based on a video game.
If Doom makes any money it will be because of The Rock (regardless of his acting ability), Karl Urban and because it has great action/special effects, etc., not because it was based on a popular video game.