So it appears that The Elder Scrolls 2: Daggerfall turned 10 yesterday. As a present Bethesda is giving you the game for free at http://elderscrolls.com/daggerfall/. I don't know if this is old news or new news, but since I just heard about it I felt it was worth talking about.
Just remember, when you start playing this game take note that it was made in 1996, so the graphics are going to look really dated. As seen from this screen shot:
Daggerfall featured a massive true 3-D world the size of Great Britain and helped usher a gaming renaissance in 1996. The full version of Daggerfall is available for download and playable through a DOS emulator.