If you played Dungeon Keeper or Dungeons then it is very similar. Lay out your digging spots. You do not have "room borders" like thsoe two games did. You could put anything in any room along with other things. The other difference is the map has levels where they did not, you have 20ish levels (minus above ground) on a map to dig to build your stronghold.
Only it does not have as much action. If you were looking for that much action then you will probably be disappointed. More fo a building/decorating game than an action game.
Well worth the $10 pricetag, I think Paradox underestimated themselves, they could have easily charged $15 and people would still been happy with the pricetag. Not quite enough content and flashiness for the $20 range though.