I second what TrevoriuS said - after escaping with the city it'd be cool to see all of your base being flooded when the power runs out. Would also encourage building multi-layered defences to see how long the base can hold up without power.
Damn, great and addicting game, but I really wish there was some kind of sandbox mode, with unlimited time and preferably really big maps, so I can dig EVERYTHING
Oh great, another game with retarded necromancer.
Why can't I wield an army of undead minions? Oh right, because they die fifteen seconds after creation.