I kind of like the fact that non-essential NPCs can be permanently killed.
On my very first play through Oblivion, I foolishly thought it would be a good idea to kill the shopkeeper at Rindir's Staffs in the Imperial City. I did not know much about the game, so I assumed that he would either spring back to life or perhaps I would be prevented from killing him at all. After I killed Rindir, I just carried on with my epic adventure.
Later on in my adventure, I became more curious about staffs. I had completed a lot of quests, explored a lot of locations and collected a lot of items. I had been playing as a warrior the whole time so, naturally, I began wondering about magic and staffs etc.
I was looking around the magic shops in the Imperial City, and I came across Rindir's Staffs again. It had been so many game hours and perhaps weeks of real time since my last visit. Of course, I completely forgot about my previous visit where I had killed the owner of the shop. So I walk in and find his corpse just lying there, exactly where I left it. After some internet research I learned that this was the only staff shop in the game (excluding Mages' Guild). There was a unique and powerful staff sold there, but I can't remember the name (Apotheosis I think).
So now, because of my actions, I could never acquire this staff! It made me think long and hard about what I had done. I think a game which makes you feel sincere regret for killing someone is a pretty impressive game. Although, my only regret was that I hadn't first obtained the staff and THEN killed him. The staff isn't even that good, but I was still shocked that I couldn't get it. At this point I was building a collection of items in my house. I'm glad Bethesda didn't make NPCs like this essential, or create replacement NPCs. It made the world seem more believable knowing that my actions at the beginning of the game could have consequences.
Oh was that offtopic? It's sort of related!
OT: It's pretty dumb when you use the old "Frenzy 100ft" spell in a crowded town centre. There is complete mayhem as civilians, mages, guards, thieves, dogs and beggars start brawling. You usually end up with a pile of corpses although you gain no bounty, and everybody ignores you. Apparently nobody saw you cast the spell which caused the deaths of all those people.... even though you used it in an NPCs face.
