The Director's Cut also includes The Missing Link and Tong's Rescue Mission DLC, as well as the Tactical Enhancement pack. All content has "all been seamlessly integrated into the narrative flow of the main game."
Deus Ex: Human Revolution - Director's Cut is $19.99 on Steam, though as a Steam Play title the version is available to all whom already own the PC version of the game.
The Mac version requires a 2.0Ghz Intel Mac with at least 4.0GB RAM, 512MB or better graphics card and Mac OS 10.8.5 or later. Deus Ex: Human Revolution supports the ATI 4850 series or better, Intel HD4000 series or better, and NVIDIA GT130, NVIDIA 9600 or NVIDIA 600 series or better.