I made this site where Steam games are ranked by playing time. It's based on data from SteamSpy with the consent from Sergey who runs SteamSpy. The value is hours played on average by those who started the game the last two weeks. I try to explain the data fields in the about section.
The site also keeps track of how many days a game has had high average playing time (5, 10 or 20 hours+ average per player) so in a few weeks we can see which games still are heavily played.
My site ranks Steam games by actual playing time
