I started playing Counter-strike in beta 3.0 (1999) with my friends. That was back in the day when only one of us even had an Internet connection (not a modem but an ISDN, mind you!) so we basically just played 5-10 hours a day in a LAN of four people. Two versus two in the most legendary maps. Most of the maps were way too big for our games but somehow that just didn't matter, it was simply fun fun and fun. Few months later I first joined an online server, the map was cs_docks (my all time favourite along with cs_backalley and the first iteration of cs_militia) and it was like no experience before. Ok, maybe Doom deathmatch in our school network was pretty comparable experience
I dare not say how big a phone bill I received two months later but rest assured, the first time our city got anything resembling a real Internet connection (cable modem), I was literally the first person in line to order one. First in line in a city of 100k people, mind you.
I stopped playing competitively back when most people were still unaware of the game, that was version 1.1 (1.3 was right around the corner). I moved on to Day of Defeat which I think was even better game than the original CS was. At least the scene was much better. After DoD, I haven't really found an online fps game that matches those experiences. CoD4 was fun for a month or so, CoD5 was fun for maybe three days. Section 8 was fun for three hours and now all hope lies on MW2.