In my playing of KeeperFX, I have noticed that several campaigns are fundamentally broken.
1. The Destiny of Ninja - Extremely poor level design (one of the levels was outright impossible), bad scripting, and a tendency to put down as many creatures as possible, which can break the game engine.
2. Conquest of the Arctic - Like #1, it suffers from extremely poor level design which makes the campaign unplayable. As well as that, there is extremely poor scripting for these levels. The most glaring example of this is Magma Land, where there are a whole horde of hero level 8 that wipe out the blues in no time and can destroy you. The only portal available is under hero guard, and the few you can get are not enough to defend your base.
3. Evil Keeper - Take Level 12 (Gotham City). The Blues are right next door to you and the gems, yet they seem to stay completely still (as in they never attack). As well as that, Level 8 (Stillertall) is a skin of your teeth level where the tunnelers jump in immediately and you have to be lightning quick to stop them getting in. ETA: Level 4 is an exact copy of Level 1. That said, where's The Goddamn Batman in Level 12?
4. The Twin Keepers - Very good level design, with few problems with the scripting. However, those flaws can utterly destroy you even if you are extremely careful such as Level 3 (Invisible) and Level 4 (where you are hemmed in from all sides.). What makes these levels difficult is the fact that you have no way of knowing what to do (even Ancient Keeper gave hints).