At first glance, the game looks as if it's a successor to Dungeon Keeper ..If you go in thinking that, you'd be wrong.
Sure, it seems to have the look that could be perceived as a spirtual sucessor to Dungeon Keeper however only the atmosphere and humour could be loosely based on Dungeon Keeper.
To summarise, you play the role of a demon known as "Baal-Abaddon", whom of which is summoned by a not so smart sorcerer named Oscar, into the lowly form of an Imp. The gist of the game is helping Baal to gain his lost powers and to terrorise the surrounding land of Ardania in the ol' "Evil is good" sort of way.
You start each level with a handful of workers and Baal, building up your dungeon with pre-laid out rooms and creating/summoning units to form squads to go raid for materials/gold/food and to defend from hero invasions from the front and/or ladders (With the addition of choosing random/fixed/no ladders, thank god!).
The game can get tedious and rather monotonous as the general tone of each level is essentially build up dungeon, build up troops, raid, rinse and repeat until you're strong enough to go into the main part of the level. The main part of the level is usually the same (With an ending "Boss" of sorts) however getting there can change from level to level. The most part is the same, however on some levels there are some puzzles which can be somewhat challenging to start with.
With the patches that were released since the release of the game, it seems to be a lot more stable compared with release. Fortunately there doesn't seem to be as many crashes/problems/bugs which was ultimately frustrating for those that first had the game as there isn't a save game as such.
On the whole, I enjoyed the game. Sure, it gets a bit repetative but I enjoyed the cheesy humour.
TL;DR - Not a successor to Dungeon Keeper but is loosely influenced by its atmosphere and humour. Game can get very monotonus and tedious but is fun at times. A lot better than what it once was on release due to bug fixes.