For those of you who aren't among the faithful, to "ace" a level is to complete it without losing even one of your adorable sackpersons. And really, shouldn't that be everyone's goal?
After playing the game for four months, we're all still having a lot of fun with it. There's always something more to discover or accomplish. The first level pack DLC came out in December, and I can only assume many more are on the way. This is just one of those games that you can play forever.