I actually played (and beat) all 3 episodes of Doom Co-Op over a 2400bps Modem. My e-peen is bigger than yours.
I've been eyeballing L4D, but I just can't make myself buy it. Money's tight, so I'm sticking to my MMO's and older stuff for now.
Also, if you truly consider yourself a connoisseur of Space Combat Sims, you better have Freespace (and Freespace 2) on your list. They made Wing Commander look like kiddie crap, and are the best of breed since XWvTF.
Also, anyone seen the videos for ARMA 2, yet? I LOVED Operation: Flashpoint and ARMA, but the tech. just wasn't quite there for what they were trying to accomplish. For those who don't know, OpFP was a military "sim" that included realistic FPS and near-simulation quality vehicle action. Damn fun stuff.