Fallout 3 difficulty was way better than Oblivion's, and if it took you 23 headshots on normal, you probably weren't using a very strong gun, or were fighting something too high level for you, or both. That's not necessarily an excuse, because as a whole, that system isn't as good as a system that makes enemies better at combat rather than having more health and taking less damage, but for the most part in fallout 3, if you were using guns that weren't horrible, the system worked in the context it was put in.
search for it on the internet, its completely detailed all the aspects of the situation the player was in, just a normal human guy taking 23 headshots from what I believe was an SMG in the vid. lets not argue technicalities, ultimately that was dumb as hell and is a testement to Bullet sponges, akin to TES....Sword sponges? lol.
and don't use the Its an RPG not a FPS line with me either, just another case of Favorable facts becoming undeniable truths. I await the day someone uses "its an RPG" line on skyrim after having an extensive record of saying its an Action RPG