ShowHN & Ask HN: Free iOS vs Free Nook/Amazon What gives?

Ok so I had a similiar app in the nook market that was released last christmas. It still recieved 100s of downloads a day and is played by at least 80 people a day. I didn't put any ads in it and its basically just cross selling our other children games.<p>This year I was able to submit a version to iOS (last years got declined as it was just another...) Its free and has an ad model. (A version just submitted adds a unlock the full game with a couple modes and difficulties). It has Game Center and Facebook integration. And its FREE! So what gives. I did a whole facebook campaign and it still is dying off with single digit downloads. I expected at least similar numbers to the Nook. So my show is this: https://itunes.apple.com/us/app/holiday-blitz-hd/id588226751 and My Question is: What are the ingredients needed to get a successful free app with some type of conversion? What marketing is worth the money?