Oh man....we're gonna have to agree to disagree about this one.
It's probably the most popular online multiplayer game of all time
....though I'm sure WOW is now. I don't play much anymore, but in college I did the CAL leagues and the matches and scrims and all of that good stuff.
I remember the original Unreal. It was always a little to Arcade-style for me. No strategy. I think I still have the CD somewhere...