Doomguy isn't technically a space marine... He is LITERALLY a space marine. He is an actual marine, not some game-world equivalent of the marines, they are actually just called marines. And they send him to an assignment on Mars as a punishment (or just because they need more marines in Doom 3), thus making him a space marine. Doomguy is actually the only true example of a space marine in a game that I'm aware of; it's all the other characters that are only technically space marines.
Anyway, yeah. I know I never said any of that stuff back when I was playing Doom. Hell, I still don't say any of that stuff when I play Doom. As for Bulletstorm, I died in the demo because I didn't stay in cover enough. I guess it was my bad for thinking it was more of a Doom type of shooter rather than a Gears/Uncharted/Killzone/huge list of games that want you to take teh coverz here type of shooter. I still want to try it again on PC though, because I kept feeling I'd have better luck getting good skill shots with a mouse. I was doing quite shit with a controller. Yeah I was still killing dudes, but I wasn't getting any of the fun combos.