Dungeon Keeper 3? Not even close.
There is very little in the way of in game content, I will attempt to cover it here.
You control a character called "The Dungeon Lord", who is controlled via point and click mechanics in typical isometric style. Your dungeon lord can cast a hand full of spells, explore the narrow pathways of your dungeon, and kill heroes.
Heroes are your main source of income, they enter your dungeon at timed intervals from a "Hero Gate" which is simply a spawn point. Killing them gets you gold, and however many "Soul Points" they've collected.
Soul Points are used to decorate your "Dungeon" with props, props increase "prestige" which unlocks new objects and gives your Dungeon Lord a passive stat buff, heroes also walk to to props and look at them (that's all they do) which can control their movement somewhat. Soul Points are also used to level up your Dungeon Lord in Sandbox Mode, making them the primary currency of the game.
To get Soul Points, you have to fill up the "Happiness" bar for the Heroes who spawn in your dungeon. To do this, you place chests of gold, monsters for them to kill, and a library or armory for them to use, and maybe a trap or two. They wander around the hallways of your dungeons picking up gold and such, and when their Happiness bar is full they attempt to leave (without warning), so most of your time is spent watching them. Once they have full Soul Points, you then move your Dungeon Lord in to kill them, and that's pretty much it, the entire game explained in this single paragraph.
If all of this sounds interesting to you, trust me it's not. There are very few monsters that you can place and they really don't do anything other than fight heroes that come near their spawn point, which they are practically anchored to. Your Dungeon Lord main character is very uninteresting, you won't be carving out many cool rooms or seeing much action in this game. The whole game is very slow, very tedious, and very unrewarding to play.
The worst part about this game is all the obviously untapped potential, if it had taken even half the lessons from the Dungeon Keeper series it could have been an enjoyable experience, but all it really kept was the aesthetic theme.