Yup, PC only.
I just finished the game (I was about 3/4 of the way through when I first posted about it) and the ending is great. The model of the final boss was a little cheesy and blocky (looks more like its from the half-life 1 engine), but the fact that they even had a final boss and is pretty awesome.
Valve should hire the people that created this is create an official expansion to Portal while the original Portal team works on Portal 2.