I have to say I really get annoyed when an npc gets on my nerves and I cannot kill them. It might be something they say or just for rp sake.
Would it be a good idea in future game to have an option when you start the game to have an "intended" game or a "free for all" game?

Intended being major npcs cannot be killed as per usual and " free for all" being that you can kill anyone but you receive a quest failed message or better still no message saying quest failed just something like " you get a strange feeling they were of importance".

So, you just want New Vegas then?

Yeah that would bring back some morrowind memories lol
Also why not allow us to drop quest items?
no just jooking dropping quest items would be stupid.