One's a puny 20 hours that you play alone, finishing the whole game in a day or two.
That's totally wrong. I've played SMG for weeks, due to replaying it and so. I also didn't play it alone, but with my friend. I can guarantee (well not actually) you that most have played it with a friend/family, and for more than a week.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS