Just a gripe about Halo: Reach here, but apparently you can very easily cheat in Firefight. My brother went ahead and got just about all of the achievements with his friend who showed him how. I won't say specifics, though it's no secret and isn't against the rules since it is using in-game mechanics (which makes it that much more absurd). It boggles my mind that Bungie would let that go on. The achievements are one thing, but apparently you can get quite a few of credits as well, which obviously effects the other game modes.