Chopper 2 is an excellent helicopter game for the Mac. Honestly, I have to say this is one of the best Mac games I have tried in a long time. I would even put it in a top 10 with Limbo and Braid. The game lets you control a helicopter, and you have to complete all types of missions across different terrains and weather conditions. There are search and rescue missions and lots of find and attack missions as well.
The game can be controlled with the keyboard, the mouse or an iOS device. The helicopter has a cannon and it can also drop bombs.
In the first few missions that you can play, you will be asked to find hostages or rescue people and take them to a base. These missions explain the controls and the game basics. After a while, you are avoiding enemy infantry and attacking different objectives, which is a lot of fun. As you progress through the game, you unlock different maps and different missions.
My favorite thing about this game is the iOS remote control. If you have an iPhone or an iPod Touch, you can control the game with your device's accelerometer. You tilt the phone up to elevate and down to descend and to the sides to move. You tap and drag to shoot the cannon, and tap on the bomb icon to drop bombs. This is implemented in such a good way that it feels really natural and fun.