For PC let's not forget Kongregate. While it may take some searching, there are quite a few well done games on there. Contract Wars is a highly detailed game if you're into First Person Shooters, there are quite a few puzzle games, at least one online Risk type game, and all sorts of things to make you chuckle. I remember playing a game where you were a penguin trying to fly!
Steam has numerous Free-to-Play games as well. I like Gear Up, it's a colorful little competitive multiplayer tank game.
The only downside I could see to PC gaming is that if you play more advanced games, the cost of a system required to run it might be more than other ways of playing. However, with the steep discounts at Humble, Steam, and GOG, and with all the free games that are out there, you could very rapidly recover the cost and come out ahead. Especially if you look around and find a good system being sold at a lower price.
