According to Doom's twitter account, it will take about 13 hours to complete the game. I think that's a pretty fair length for a game like this. It seems like a pretty average length. I'm sure it will have some replay value as well as the harder difficulties.
It's fast pace and hearkening to the original Doom are going to make this game something pretty special though. I'm one of those people that doesn't play a lot of FPS games but this is one I'm looking forward to. And now that they announced the collector's edition I suppose I ought to start saving up. 13 hours of Doom goodness sounds pretty good to me.
What do you think? Is 13 hours a good average time to get through the game?