Painkiller the Mindkiller

I'm ocationaly look at the game Painkiller, and wonder what they were thinking. At time you have both Knights templars and ninjas attacking at the same time, other points WWI Germans and skeletal imps. I've heard the expansion has clowns and zombies. What were the creators thinking treading onto Serious Sam's territory. This game makes no sense, but for the mindless eye candy experience, its worth a shot. At least its better then Doom.