a)
Not really a problem on PC, but I know that can be annoying. I really hated when multiplatform came on PC with unlocked difficulty levels.
b)
Oblivion adds just about nothing but hp for enemies when you crank up the difficulty. Only harder thing is with harder difficulties that you need more weapons, because your weapon will break per one enemy because you need to hit them thousands of times.
c)
Well, I prefer games that are hard and have no difficulty levels, because theres always some idiots who say its too easy on easy.
d)
Isn't adding more hp/damage for enemies cheap method? :)
Somewhat related article,
http://www.gamesetwatch.com/2010/02/analysis_is_hard_the_new_good.php
@Mummelmann
I hear you, man. I really don't like either 'teleport all your members into one blob to die'. Especially because I usually take the stealth approach.
And unlimited spawning. Uh, oh. Thats one of them most annoying thing when you have limited ammo.