A True Classic
Being an older game, its maximum resolution is only 800x600, but the charm and overall feel of the graphical presentation soon made this a non-issue. The sound is also excellent, with a great narrator and all the requisite sounds and effects you would imagine in a underground lair setting.
The basic set-up is that you are the evil keeper of various underground lairs, battling for dominance against the forces of good. This alone makes the game fairly unique - how often do you get to play as the bad guy! This game will have you being bad and loving it.
The game play consists of expanding your lair by carving out rooms from the surrounding rocks, and building rooms to attract different creatures to your dungeon. Each mission tasks you with defeating the forces of good to obtain their portal gem, along with various sub-quests and other hidden secrets.
One interesting feature that sets this game apart from the standard RTS is that you do not directly control your creatures - they have their own agendas and will respond to environment depending on the circumstances. You can, however, pick up your creatures and drop them in an area, where they will proceed to attack enemies, use the training room, research spells, or whatever the most likely task for their type happens to be. Beware though, they still may not always do exactly what you want! Another amusing feature is that you can slap your creatures with your hand to make them work harder, at the expense of a small hit to their hit points.
In addition to your creatures, you are also able to research various spells, and craft many items in a workshop; such as doors, traps, and defensive emplacements. You can set up some nasty combos by placing these items in a strategic fashion, and set up kill-zones to assist your creatures against any unwanted incursions into your lair.
Overall this is one of my all-time favorite games, and while Evil Genius is a more modern update of the same genre and excellent in its own right, I am still disappointed that no more sequels were ever made in the Dungeon Keeper franchise. I cannot recommend this game enough!