There has been quite a few games this gen I've dumped an insane amount of hours into. First and most obvious is WoW, depending on what we mean by "this gen" that time amount changes. From launch, though, I have close to 10,000 hours clocked in.
Past that into normal non-mmo game territory the second highest would be the collective Pokemon Gen 4 games. 400 hours into Pearl, 350 into Platinum, and something like 30 into Diamond, so nearly 800 hours between the 3 games. Minecraft comes in second with around 400 hours total (I've actually been playing in the same single player world for almost 2 years now! It's amazing how much I've done in that world). After that Pokemon Black comes in at around 350 hours, Final Fantasy 12 (if we're including that as well, since it came out in late 06 for us) with around 300 hours, and then Final Fantasy 13 at around 200 hours.
There are a few other games I've sunk about 100 hours in like Civ 5, L4D2, Last Remnant, or Binding of Isaac, but 100 hours is pretty measly compared to anything listed above.