There are thousands of free browser-based games on the internet that you can play from your PC for free. However, the quality of the games is very variable. Some are superb, others are very poor.
Friv is a simple web site that offers a direct gateway to 250 excellent browser-based arcade games. Just go to www.friv.com and hover your mouse around the icons to find a game that you like, then click to play. In each case, there's a link back to friv for when you feel like trying a different game from the selection.
If you're in the mood for playing games, just head to www.friv.com.