I think it's a great combination of skill and luck. It really makes you think in order to get the bonuses. My only gripe is that I sometimes accidentally pick a bomb, instead of cards. Then, there's no way to un-pick the bomb. That can really screw up a game.
What is everyone so upset about? There are over a thousand games you can play for free. If you don't want to buy the full version, then don't. But, I don't see anything wrong with offering that option to purchase.