HOLY SHIITE!
I... Friggin' hell dude, I just saw a behemoth. On the first screen.
I had gone out for a little looting spree, and after a couple screens I saw the first green dude that people keep talking about. I was looking forward to splattering it for the XP and loot, but I ended up walking out of the screen while I was fighting him.
I went back in but only found a bunch of aggro'd non-green zombies, so I figured I'd just head home.
Back one screen... There are three bots milling around and unloading every single bullet they've got into a TIDE of running zombies. I managed to run back to the starting screen connection point with only one hit, but that was with some rather fancy footwork.
So then I'm back, and I think "safe and sou-" and then I see this HUGE red titan running at me, and there's a loud boss-music beat accompanying his presence. I turned around and went straight back to the second screen.
I figure that's probably removed him, so I venture back in... Everything looks nice, and then out of absolutely nowhere everybody gets aggravated. I get hemmed in behind a bus with running fatties on either side. I figure I'm more screwed than a nail.
For those who are looking for a nice and easy way out of a tricky situation, press the "back" button on your browser.