For me it was love at first site. I saw a Tekken arcade cabinet in 1995 and only played it once (There waren't too many arcades where I live, even in the 90's). Then I saw it running on PlayStation in summer of 1996. I couldn't believe that such a graphical juggernaut of a fighter runs on a home console. Tekken was the game that made choose PS over Saturn, it just looked so much more awesome than VF. I played Tekken ever since. Unfortunately thse days I don't have as much time as I did during T1,2,3 times :/
The good ol' days with Galaga in T1 and Tekken Ball in T3.
Played T1 in the Arcades, and every Tekken since (except TTT1), so it's got the major nostalgia factor for a start. Been playing all this time and I'm still more of a noob on it than a lot of people who probably started with T6, or even TTT2, but no worries, I do try to learn slowly.
What kept me hooked from the very first game though, was the number of moves, and for some reason I've always loved the throws. Where most games throws where generic over the shoulder ones or knees to the groin, Tekken has always had some amazing looking, brutal grabs. It's why I fell in love with the King characters.
Same with "stances", characters like Lei have just always been fascinating to play as or watch, more so than other fighting game characters. Most of my juggles end up as "jab, jab, big whiff", and I my w/l ratio is shockingly bad, but I will always love Tekken.