Who says you need completely novel gameplay mechanics to charge money for an app? Surely more polish, hand-built levels and an app are sufficient. Whether OP would make more on ads or IAP remains to be seen, though. An IAP to get more levels would be a good way to hook users.

The overwhelming majority of app users would not pay a cent for any app, much less a game.

Free sells.

People charge for Chess apps. :)

Angry Birds wasn't a new concept either.

I was looking for this, I knew I had played it before.

This one has much better controls on the web app, as well.

exch, you point to the mother of all "we stole your game play and made a new game" sites. :)

I saw someone charging for a game based on the exact same principle last week. No reason not to.