From the directory listing:
Shoot the three biggest whitetail bucks you can find (per site) without hitting any does. But be careful -- innocent does and crafty critters will try to distract your keen hunter’s eye at every step. With a combination of kill distance, impact location (where you hit the deer), and number of shots for the kill, a skilled hunter can achieve Big Buck Hunter Pro glory.
The game mechanic is very simple and relies more on reaction than careful planning. It's a style of game play that worked well in the arcade, when you were able to hold an physical rifle, but does lack the urgency or feeling when translated to the touch screen of Windows Phone.
We'll have a full review next week on AAWP once we've had some time to play through the game, but for the moment you can pick up the trial version from the AAWP App Directory, or the Microsoft Store.