Looking at all you with these things in the 300s I feel slightly left behind with my 156 hours of Crusader Kings 2 as my highest.
Though that said 80 hours of that were in the first 6 days I owned the game.
I mean it just depends a lot on the game. Some games I don't play frequently but have had a long time, like civ5. I play it in spurts like a 10 hour game here and there but it's been out 3 years almost so it adds up. Dota 2 is definitely my biggest obsession though, I've only had it 7 months.
Other games you get to 30 hours and they're completely done, no reason to play anymore. Like batman arkham games. Awesome games but once beaten no reason to replay.
I actually sometimes wish I spent less time on singular games and tried to finish everything in my library at least once. There are so many games I haven't even turned on in my steam account I didn't list.
Since we're doing offline estimates, some of my tops:
Mass Effect 2 ~ 100 hours
Dragon Age Origins ~ 100 hours
Civ4: BTS ~ man I dunno, it has to be over 1000. Maybe close to 2000. I mean I've had the game 5 years and sometimes it's the only thing I played for an entire month.
I have a lot of other games that I never quite got into like mass effect 1, assassin's creed, the witcher, obivion. All under 20 hours I'm sure. But the bane of my existence from 2004-2010:
World of Warcraft ~ 10000 hours. How did I arrive at this estimation? I literally played this 50+ hours a week in college. I didn't watch tv, I didn't play any other video games. I worked and went to class but weekends I didn't leave my house. It was bad. In wow you can see time played per character and it's measured in days as in 24 hours of time logged in. I had multiple guys with over 80 days. It took meeting my wife and all my friends quitting to finally kick this game. I'd actually still be playing it if it were fun but when you can commit to 5 hour raids and you don't have any friends on your server it's a pretty lame experience.