Oh boy, listing~
To give a bit more insight briefly into my list...
01.) RPG Maker VX Ace - 2,369 hours:
I've made a few games in it, experimented with it, learned it. Honestly, some of that time is me being lazy and leaving it on overnight or leaving it open while I study into some things, though.
02.) Gmod - 250 hours
My friends love playing it too much and I usually end up being the one hosting servers.
03.) Killing Floor - 237 hours
My all-time favorite arena-shooter, though KF2 is shaping up to be even better. Modding scene made me get a lot of use out of it, and the higher player count (6-player normally, can easily mod in more).
04.) Left 4 Dead 2 - 196 hours
So many custom campaigns worth playing~ Also near everyone owns this game, so easy to set-up with friends and play.
05.) Resident Evil 6 - 149 hours
I actually like it! But I've played through the game a couple times on PC all the way through, various smaller parts of the campaign, plus have played Mercenaries quite a bit along with the multiplayer modes, so it adds up.
06.) Terraria - 92 hours
Friends like to play it, so I play sometimes when they ask. Games like Terraria and Minecraft drain me for some reason, though.
07.) Team Fortress 2 - 91 hours
I had an older account that played much more TF2, but got hacked since I was dumb back then. Have played a bit here and there, but not recently.
08.) Borderlands 2 - 66 hours
Played by myself all the way through, played the DLC with others, slowly over time making my way through it with a few friends.
09.) PayDay 2 - 64 hours
Heisting with friends, really. Haven't played it as much as some of my friends though, jeez...
10.) Resident Evil Revelations - 59 hours
I played my blind run on Infernal, so that took some time. But most of it is from Raid Mode, Ghost Ship and that mode can be addicting.
11.) Resident Evil Revelations 2 - 57 hours
Most of this is actually from the campaign, though a fair amount of Raid Mode. Played the campaign twice, quite enjoyed it.
12.) Resident Evil 5 - 48 hours
This was my most played 360 game, on the 360 I have something like 700 hours in RE5. Friends kept asking me to play with them when they got it, I always said yes, so I kind of know this game inside and out at this point. XD; Recently beat it again with Steamworks so I could have the extras unlocked for when friends want to play the DLC with me sometime.
13.) Evil Within - 45 hours
Believe it or not, that's mostly just normal play-time. I've only beaten TEW once, but the playthrough was close to 20 hours since I took my time with a lot of things. I played a bit on Akumu, pass Chapter 6. I got all the map fragments. The rest of the time is from the DLC, which all-together probably took me around 12-15 hours to beat all three pieces of DLC, taking my time of course.
14.) Deadly Premonition - 45 hours
Played and beat on the 360 and PS3 before, Steam version is the first time I did all the side-quests though, so that time is me playing the game and completing all the side-quests.
15.) Alan Wake - 45 hours
I have a strange fondness for this game and go back to play it all the way through every couple years. I've beaten it something like two times all the way through on 360, two times all the way through on PC, and I always take my time and explore in that game.
---
Less time than some, but as I said last night, I jump a lot between games. I play a lot of different games and don't spend usually -too- long in any single game.