When it comes to the normal PC-gaming experience I expect, Windows 8 delivers. However, after running a dozen or so games, I did encounter some minor issues, as I noted earlier. Older games may have problems, particularly those titles that use obsolete, driver-level DRM schemes. Current-generation games should mostly be problem-free.
Although the vsync issue with Crysis 2 is a concern, it didn't seem to affect my subjective gaming experience at all. However, if you have a lower-end gaming PC—particularly if the GPU is underpowered—the vsync lock may introduce some stuttering. Other games I played don't seem to have this problem; this is the only title I've encountered so far that does.
What is not an issue is performance. Most games under Windows 8 seem to perform as well as they do in Windows 7. Some may perform better than expected. In the end, Windows 8 may introduce problems in some games at first, but most games will likely run just fine, and game performance on Windows 8 will in most cases be equivalent to performance on Windows 7.