All good stuff here, just want to add a few words.
Aces High is not a game... it's a place to meet with other players to play games. There is a basic goal, for three teams to capture each other's bases. But there are almost an unlimited number of games happening inside the main game. Players get together and do what they enjoy best. The main feature of the game is personal interaction... working together with other players.
You can spend hours defending a single base, or attacking another base. You can participate in large missions and capture many bases. You can work with planes, guns, ships, or ground vehicles. You can dogfight, tank fight, be an ainti aircraft gunner, attack bases with tanks, bomb with dive bombers, or drop large salvos of bombs from huge bombers.
Fighting other planes is the most demanding thing to do. Great skill is required and the are many highly skilled players to fight. Learning will seem slow and the more you learn, the more you will realize you have yet to learn. You will be killed mercilessly and often, the frustration level is horrific, but this makes the occasional kill all the sweeter.
Used properly, Aces High is not a game but a life style and social structure. You don't play Aces High, you emmerse yourself in it. Your life may never be the same.
I hope you enjoy it greatly.