"Shadow Of The Wool Ball" is a first person shooter similiar to Wolfenstein 3D or Doom, though a lot less gory. You take the role of hedgehog Scott, who has to save his girlfriend from the clutches of an evil empire of space kittys that has enslaved his entire home planet. The game contains 18 levels, split up into three episodes.
This version does not need the original Doom files and can be played on it's own. ZDoom v2.7 is bundled with it.