Exactly my first experience. I walked in on my roommate who was playing TF2. I said "That looks fun."
Note: I had never ever played a First Person Shooter before. Ever ever.
I downloaded it, at about 6PM on Friday. I woke up with keyboard impressions on my face the next mor...afterno...evening.
I then racked up about 50 game hours in two weeks. I'd come home, sit down at my computer, and play TF2. Time was taken for food and youtube, and that's about it.
My computer went from 'boring work station taxed by Firefox' to 'monolith from 2001' in one month... for TF2.
I've since branched out, but yeah... TF2 for me.
And in about 6 months my house WILL have an intel bunker.