How stupid is this. I have Batman - Arkham City. The download installer lets you select an alternative download location for the game's install, but if it isn't downloaded to the default C: drive location, and your custom location has any spaces in the directory, the installer fails right at the end with an "input string not correct format" error.

Removing the space from the directory and the game installs fine.

Why can't games developers just all use Steam!