Very good game. It is in beta right now but it is free to play. LINK
About 6 gbs.
There are objectives your team has to do (bomb an airfield, aa guns, tanks etc.) Or you can just do dog fights. I think it is about 15 v 15 every game. You can choose between Japs, Muricans, Brits, Nazi's, or Russians. Each has a different set of planes that do different things. You can choose between Bombers (easy to take down but can do some damage on high value targets) Attackers (A combo of fighter and bomber) and Fighters (for dog fighting).
You can choose to spend money on gold (don't have to) which can help you upgrade your planes. Not necessary because if you are skilled enough at flying you can just level up.
Some game play- LINK