I've been playing in a casual Counterstrike clan the last several weeks. I've always been complete rubbish at first-person shooters (FPS) but that hasn't stopped me. My stats are slowly - very slowly - improving.
I'm no fan of FPSs. Never finished Far Cry or Half Life 2. Both are visually excellent but I can't find the motivation to stick it out. The only FPS game I really stuck it out with was Halo and that was because Jenny and I played it as a team. What's attractive about Counterstrike is the team play. It a very well balanced game. What's surprising is that nothing has surpassed it for the most played FPS on the 'net.
I also had a play with Hammer which is the 3D tool from the Counterstrike: Source SDK which allows you to create and edit maps. Very cool. Didn't take much for me to make my own room and play in it. I can see a big blackhole of time sucking activity there! Great way to get into 3D modelling.
The clan is also trying out Battlefield 2 although we're not very co-ordinated with that yet. It's very impressive. I once went on a public server with 60 other players fighting a pitched battle and it was manic. It's certainly felt like a war simulation and would be addictive if you played with the same bunch of people regularly.