Sky Force 2014 is another family favorite in our household. Truth be told, the Husband enjoys this one more than the kids. It is a first class arcade style game that is very well made and gets great reviews for a reason. The app if FREE, but has in-app purchases that are not required (but you will be tempted!). It has seven different levels with three difficulty options. You can level up and earn upgrades to your shields, guns, missiles, lasers, mega-bomb, etc. Save the civilians and get even more!