Let me first say that this game is great. The story and characters are fantastic. In fact, they are all that is keeping me playing at this point.
I bought all 5 episodes through steam and am playing on a 2010 Macbook Pro. I've got Snow Leopard as an OS, 4 GBs of Ram, and the dedicated Nvidia card on. Not a hell of a rig (what mac is?), but enough to play this game.
The game runs absolutely fine on 1440X900 on high or low settings, but is subject to constant freezing whenever it autosaves. At EVERY autosave point in the game, it locks up for 20-30 seconds before continuing. This completely ruins the suspense and tension of any action scene. The music continues, but the screen remains static. There is no way to turn off autosaving either.
Worse, perhaps, is that the game crashes about every hour. Sometimes, it does not record autosave data at all. I now have to do almost all of episode 4 over again because it decided to crash and revert me to an autosave at the end of episode 3.
I would hope that Telltale reads their own forums and have recognized that there is a serious issue with the Mac version of their game. Reviews, both from professionals and customers, have pointed out numerous times that this version has significant technical issues. I would have hoped that by now, by episode 5, there would have been an update.