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 Is now considered sadly outdated.