Despite not playing it for months now, Awesomenauts remains my most-played game ever. Well over a thousand hours. I don't even know how much, as I played it on PS3, my in-laws 360, my Steam account, my brother's Steam account (splitscreen), and the same deal with the in-laws.
It was the first online game I got into, and I have an addictive/obsessive personality, so..
I hope for nothing to ever top it unless it's literally the only game I play for the rest of my life, or I play it (hopefully happily, and not out of addiction) for a few minutes every day or something for a number of years. The time is straight up unhealthy.