Essential Characters have to be the worst idea ever introduced into the Elder Scrolls series. I still can't fathom why Bethesda ever thought invincible characters would be a good idea. It was an awful mechanic in Oblivion, yet here we see it again, in Skyrim. Nothing breaks immersion worse than trying to assassinate someone and seeing them drop to their knees, unscathed by the dagger you just shoved into their back.

Why exactly did Bethesda implement this completely idiotic idea? If players want to go around killing NPCs, the game should let us. We shouldn't be unable to kill a character just because they are involved in a quest. Even characters involved in minor quests are invulnerable. A heroic character can't barge into the Thieves Guild and kill off the members, because half of them are invincible. Evil characters looking to assassinate someone have no way of knowing if the person will actually die when they hit them. It's a stupid idea in a game that advertises the ability to do anything you want.

I know some people might say that they like essential characters because it breaks quests, but really, if you're gonna go around killing random NPCs, you should be ready to face the consequences. While it's possible wildlife and dragons could kill off quest characters, why couldn't Bethesda just make quest NPCs unable to be killed by wildlife? This is the easiest compromise and ensures that quest characters will survive as long as the player doesn't deliberately kill them.

I remember in Morrowind, killing main quest characters would show a message something like "this character's death severs the thread of prophecy". I'd really like to see this type of system implemented again, because essential characters has to be the worst type of hand holding mechanic ever put into the game.