I am going to go with the Medal of Honor series, primarily the Breakthrough expansion.
My summer day consisted of waking up at around 10, playing the game. Eat dinner, play game. Night is coming, still playing. End playing at 3 - 4 AM.
I knew I had to stop playing when I (literally, not in the game) walk into my room and, in an instant, spot someone in my room and quickly go for my rifle. (Yes, I jerked my hands towards the bottom right area of my body to pull out a rifle :-| )
Same went for grenades. I have more than once thought about tossing 'nades when I'm in a room with lots of other people.
I stopped going out of the house; this game was too good.So, I don't know what the addiction factor of that would be; perhaps a 10?
Give me a Carcano, or a DeLisle, throw me in rotating objective maps, have realism enabled, have mustard gas grenades enabled, and I won't leave the
PC.
To clear confusion, NO I am not one of those people who go around bombing or suiciding and all, lol; I am merely sharing what was the cause of an addiction to an FPS.
This is Medal of Honor, and anything else is unimportant.