I wanted to play a seedy, murdering sociopath, but the first NPC I attempted to kill--a random woman in some farmhouse--I discovered she was essential. I promptly deleted the character and stayed away from the game for a few hours. OP, I hear you. It's a bit over the top.

Consequences of killing an "essential" character in Morrowind were pretty cool, I thought. It was nice that you could kill practically anyone. However, there was a major glitch where some "essential" characters would disappear, presumably victims of collision bugs and trapped in a graphical void. So, sometimes, even if you didn't intend to lose or kill an important quest giver, the hungry graphical void would svck them into their earthen grave never to be seen again.