My game installed without any issues, but when I logged into steam and tried to launch, I got as far as a message saying 'Preparing initial setup' (or similar); after which the splash screen came up. However, the game did not launch - in fact nothing whatever happened. In addition, attempting to start the game via the exe file (which you're not supposed to do folks; testing reasons only here!) brought up an error message saying and audio dll was missing.

Sound familiar? If so, try the following:

Find the Steam folder (in Program files), then locate the direct x 10 folder in SteamApps. Run the dxsetup file to force the program to install dx10.

It took my boyfriend - who is in web development and codes for a living - over an hour to find out that the game was simply failing to complete updating my machine to directx 10 (I generally run dx11 being on a 64bit os), thus the whole thing wouldn't run. I have no idea why this occurred, and evidently it hasn't been a problem for most folks; but I thought it worth posting if I could save anybody else the pain...