games which got me hooked have mainly been fps games.
spanning online gaming from 1995 to present day: duke nukem 3d (wireplay), quake(wireplay), quake2 (wireplay, later on net), quake3 (net etc).
I was hooked on duke3d as I could make maps easily and it was the first competitive online game I played, being able to win up to £20 every 2 weeks or so on wireplay. Aswell as a good community.
I really got into quake2 due to the weapons etc, later on I joined a clan and ended u playing to around about 3am in the morning. IMO it was the best online game so far and always will be. There was an excellent community, very little bitching or progamer wannabe's.
Quake3 I really didn't like at first, it just looked like marioland or disneyland with all the colours. Gameplay/netcode wasn't so good on release and at the time there seemed to be a massive amount of people trying to become progamers and cheating.(I guess they moved from counterstrike

)
The main reason I got hooked was community and my friendship with my clan. It slowly broke up as the original members left tho, then Rocket Arena really got me hooked. Deathmatch in quake3 was no where near quake or quake2 and ctf+tdm was dire.
After being hooked on all 3 of the quake series I was very dissapointed when quake4 came out with all its bugs etc

fps gaming really seems to have taken a nosedive, both in gameplay and community. I guess we'll never get the days of quake/quake2 back.