Maybe my friend and I are just good at the Halo 3 campaign, but we blew through it on legendary like it was nothing.
It's not that bad if you realize most of the enemies won't advance on you (at least they wouldn't in H2).
Also FUCK Left 4 Dead on expert. Me and a few guys got to the end of Dead Air with little trouble (The second to last one was hard because of the massive open zone and the parking garage near the end, you get a horde rush out there and you're damn near fucked) and when we got to the end we would almost ALWAYS die off on the first tank.
There isn't a ton of room to run, he can OUT RUN YOU EVEN WHEN YOU HAVE FULL HEALTH, he has a metric fuckton of health (like near twice what he has in normal) and he has other boss zombies spawn when he's around. So basically you and your team have to run in small circles together while constantly shooting the tank and watching for boss zombies.
I probably wouldn't have trouble with this other then the fact that boss zombies spawn and your team almost always splits up, and boss zombie + team split up = a quickly dead team.