When it comes to the PC gaming, the sad truth is, that if you want the best games out there, you will have to either buy them or download them from the spooky dark web. You do have some free games like League of Legends, DOTA 2, World of Tanks, Smite, ... but if you want the games that end up winning the game of the year award you will have to buy it.
Let me put it this way; if you buy the game, you have thousands and thousands of different games, from any possible imaginable genre but if you want the free game then you won't have as a big of a choice. You will have to be satisfied with what you can get.
I prefer to just buy my games since I play things like Witcher 3, the Final Fantasy franchise, OverWatch, Life is Strange, MGS franchise.