A month ago, Nvidia released the beta release of Geforce Now, a streaming service that allows you to play demanding PC games even on a slow Macbook as long as you have a fairly fast internet connection.
Betan was about only US users, but now the company has also opened to players in Europe and as long as it's a beta it's free to test.
Geforce Now installs and runs all heavy calculations for the games on Nvidia's servers. Entries are captured on your computer and the finished image is sent back. Everything is so optimized that in a fast connection you hardly notice that the game is not running directly on your computer. And in comparison to the graphics settings you're usually forced to use on Mac, they look very good.
The actual games you have to own yourself, unless you choose freemium games.