I bought this game today in the Mac App store. I'm running it on a 27" iMac (late 2012) with 32GB RAM and the 2GB nVidia card. Overall, the game is great and I'm really enjoying it.
However, I have multiple monitors connected to my iMac. If I'm trying to look around an area in free range mode, the only way to do that is to move the mouse to the edge of the screen, at which point the game begins to adjust the scene.
Except, when I do that, the mouse pops onto another display and the game stops responding. This is kinda frustrating.