RA3 is where I started my interests in first-person shooters. My family and someo of their friends had a clan, and they would hold LAN parties, playing matches against other clans. Sometimes I was allowed to play a bit, and got instantly hooked.
When I got my first personal computer, I stated playing RA3 a ton–and Unreal Tournament on the side. Later on it became Quake 3 OSP/CPMA (as well as Freeze Tag and InstaGib) and Quake Live Clan Arena, but never really competitively.
At the same time I also discovered CS 1.6. It was sort of a relaxation from all the fast-paced fragging for me. I liked the slower pace and different skill it required. I eventually joined some tournaments and started playing more competitively, hooking up with people in IRC.
I try to seek out games every now and then, but unfortunately there's less and less communities around Q3 and the likes, so it's becoming increasingly harder to find fun matches.