it turned out to be not free,
USD$ 120.00 per named user, or
USD$ 5800.00 per processor
and if you want to deploy your app say to app store you need processor license.
Oracle FAQ :
A named user plus license of ADF will entitle customer a single
named user license of the ADF Mobile.
A processor license of ADF will allow customer to deploy ADF Mobile-based application to
unlimited number of devices.
I'm still though unclear about whether it's suited for games but there is a hint :
Oracle FAQ: You may even add a feature based on
device-native code. All of these can run within the same application,
and all of these features can communicate with each other.
hope someone else shed more light more about making games with ADF mobile.