A computer game with optional PvP (battle.net) abilities. Highly addictive. It has regular levels (will take you a few years to beat them all unless you play regularly) and also extended 'Dark Portal' levels. You can choose to play as Humans or Orcs. The Dark Portal levels regularly feature NPCs, while these only appear from time-to-time on the basic levels.
Available are custom maps, which allow you to play only one level of any given situation. Some even let you upgrade for free! If you have Map Editor, you can create and use your own maps.
Until you get far enough in the game, it can be really boring. However, once you get the hang of armies and using Death Knights, Mages, etc, it is very easy to enjoy.
Went on sale for about $35 CN three years ago. Is now considered sadly outdated.
I am so old school that I do not play normal computer games; I play Warcraft II.