I agree with the first point a lot. You never feel too threatened in halo, so it feels less satisfying. Maybe the aggressive tactics (searching for a weak player, throwing grenades) should be more prevalent on higher difficulties.
MW2 seemed like kind of the opposite; you generally felt too vulnerable. You had to camp in cover until the next wave was dead, then move up and repeat. If you broke formula, you died in less than a second. While sometimes I felt accomplished in advancing and taking an enemy position, more often than not I felt undue frustration at being the only person targeted by a score of enemies while my squadmates did jack to help me in any way. While it might not be hard to take down a scarab, it is sufficiently complicated and there is a big enough explosion that I do feel good about killing it.