Do you like the old DOS shareware games like Hexen, Doom, Duke Nukem, etc.? The get your game on here where you can download them for free!
http://www.dosgamesarchive.com (http://www.dosgamesarchive.com)
EDIT: btw, you'll need DOSBox installed to run them since they are DOS based games:
http://www.dosbox.com/wiki/Basic_Setup_and_Installation_of_DosBox (http://www.dosbox.com/wiki/Basic_Setup_and_Installation_of_DosBox)
It says to use v7.2 but that is an old version so use v7.4 for your OS.