After playing Day Of Defeat, version 2.0 this weekend, all I can say is "WOW!"
I've played the previous version, and it was a good game. The amount of stuff pumped into this new version, however, is enormous, allowing a much different experience.
For the first time, I find myself slowly advancing the line of combat, ducking in dark corners, trying to avoid an onslaught of nazi's. I, actually, was getting nervous in my seat while I played some of the maps. The amount of realism is incredible (but still being fun), the way they balanced the game is GREAT, but most of all, the "feel" of the whole environment is EXCELLENT.
I have a feeling many lost hours of sleep in my future will be due to this halflife mod!