You mean the chaingun? I don't know if I ever noticed it pushing me back, maybe it's because I pretty much always crouched when firing it, since that improves accuracy drastically.Opposing Force is pretty awesome. Only game I've ever played that a gun actually continuously pushes you backwards from all the recoil.
I'm playing TF2 again I'm sad to say lol, I don't know how many times I've deleted that game off my harddrive in frustration. I'm TRYING to just play it casual-like because that makes it more fun, but I also want to win (and I'm not super duper awesome at aiming, meh), so sometimes it's hard to rein myself in, and then I get incredibly pissed off when I get 1-shot gibbed 5 times in a row within like 10 seconds of leaving spawn.
TF2 would be a lot more fun on the whole if all weapons simply did 50% less damage, but the kiddies today have no patience... If the enemy doesn't die in 1 hit then they lose interest it seems.