Garry's mod 75% off on steam + question
So, garry's mod is 75% off on steam ($2.50), and I'm getting it no matter what. But I wanted to know: is one game that works with GM better than a different one? Eg, is it better to get CS:s, or could I just get portal and it would work just as well? Sorry, I have no idea how GM works. Any help would be awesome.