Again, I can't speak for Windows 8.1 compatibility, but it works just fine on Windows 8, which is what I'm running. I have the game installed and can play it just fine with no issues. Halo 2 is what I don't know as I haven't had it installed since back when I was on Windows 7, and like I said, I don't even know if you can still activate it since GFWL is no longer around.