I'm still a big fan of doom. I even had a stab at designing some maps using WadAuthor. Check out my nojer2wad

Here's a few things which make doom II better than more recent first-person-shooters:

• Not so many different keys to learn. Makes it easier for new people to learn (more deathmatch potential)
• Cooperative multi-player mode. Many newer games can't have this because the way they load in the maps.
• Doesn't require huge hard disk space.
• Doesn't require huge processing power.
• Can listen to mp3s while playing it.