not sure actually, but I bet Black Ops will soon take that crown

Of the games I bought in 2010 SSBB and Lunar Knights are the most played with 100 hrs and 60 hours respectively.

Of games that released in 2010: Monster Hunter Tri with aout 36 hours (I only ever played the game during the first couple weeks after launch to boot) and Tatsunoko vs Capcom with 32 hours (and only 9 separate play sessions)  I know their playtime will increase dramatically with time because lately I've been buying and completing games I meant to a long time ago but didn't have a wii to play.

Final Fantasy XIII (PS3) - 60 hours
and I don't care what anyone thinks, it's an amazing game.

Mass Effect 2, then probably Reach.

Mass Effect 2, but Fallout new Vegas is catching up.

I played it more than 60 hours hell 60 hours is basically going through it once and not doing any of the cie th stone missions. I played it to completion as well as doing almost every cie th mission (grew tiered in the end) and i still say it "sucks", about 85 hours played btw.

By sucks i don't mean that it is bad, but when compared to previous Final Fantasies except X-2 its bad.

Pokemon SoulSilver - 60 hours

How?? Its a excellent game and all but I just can't see how anyone could play it for 300 hours...thats like 10 different playthroughs!

Final Fantasy XIII, around 100 hours.

77hrs spent on Halo Reach