A mix between Dungeon Keeper and Theme park. A bit too much micro-management, but its still good.
Your mission is to make sure to make all the heroes happy by throwing monsters at them that are just right in difficulty, ensuring that they can beat them, but not too easily.
Then you create rooms filled with different kinds of loot, and traps for them to disarm. And when the heroes are filled with stories of all the mosters they've slain, and have all their pockets full of loot - you kill them, and reap your reward :)
It's a quite fun idea for a game, but in reality it sometimes feels more like farmville. The heroes are your crop, and you make sure they get all the feritilizers (monsters & loot) they need before "harvesting"... This wouldn't be so bad, if it werent for some maps requiring you to just tend to your "plants" for an hour or so, just to make you powerful enough to be able to do the main quest.
The only thing you can really control (except for the building-part of course), is the main character. Your monsters and minions have a life of their own. You just place a "pentagram" on the ground, and then they continually spawn.
So, what could have been done better?
More control of your monsters. Right now the monster-pentagrams just remind me of any old weapon in any old tower defence game.
You should be able to get an overview of your heroes, and how far to "maturity" they've come. Scrolling around the dungeon, looking for heroes, and then having to put the cursor over each and every one just to check their status is really tedious and takes focus from the real gameplay.
As a .NET develloper, it's fun to see that the .NET platform has been used to create the game. Perhaps it's finally time for the game devellopers to start using a bit more modern programming languages and environments.