Syncing with multiple Google calendars, or any Google calendars that you don't directly control seems like an unsupported feature in Windows 8 calendar app. Since I like to be able to see my wife's calendar as well as my own, and also occasionally create separate calendars for different things, this was a very frustrating limitation. After a bit of research, I found that it was possible. In the end, the workaround is a testament to how much Google has changed over the years.
How to do it
After a bit of frustration trying to make it work through Google directly, I found this workaround on Microsoft's help page:
Why its ridiculous
For an advocate of the open web, Google sure does manage to make its services hard to use on competing platforms doesn't it? I understood when Google's stuff was crippled on Windows Phone, where it has no native apps, and the web-apps are the feature phone versions. It is a niche market and Google wasn't going to put extra time and energy into optimizing it in order to help a competitor. But Windows 8 is hardly going to be a niche market. Google is actively preventing something that clearly is technically trivial. Doing this in order to discourage users from using your service on a competing platform may be good business, but it is not "open web friendly." Its Google's choice to make obviously, and I wouldn't call it unethical exactly, but they've come a long way from the moral high ground they claimed to occupy in the web space just a few years ago.