When my brother and I played House of the Dead: Overkill, we just wanted to run and gun, without too much story...at all. In a ORS (On-Rails Shooter) it doesn't really have much place. Even in HOTD:Overkill, between all the swearing and jokes, I was kind of anxious to get to the action.
From what I see in this thread, I'd imagine that DS: Extraction had loads more, which is BS. I'll youtube the cutscenes to see if its true.
And I really find it rude that it is $50 on the Wii, with glitches, yet $15 on the PS3/360 with more features and an actual...prequel y'know, with a sequel coming. Ugh, I hate test games, on all consoles. The Wii just happens to get the most.