Fresh from the Bathesda E3 conference comes the official worldwide reveal of DOOM. Check it out in all it's gory goodness below.

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[Sakitoshi]

the original games where run and gun as well, the only difference is health and ammo drops out of enemies which is a blessing considering that on harder difficulties doom can kick YOUR ASS HARD. that was the problem with the older doom games, on harder difficulties you had to be really fucking careful because death was always around the corner and with limited health and ammo you had no hope for survival unless you honed your fps skills to the max.

note to bolded part: on nightmare difficulty ammo pickups grant double the ammo it normally give and you take normal damage from demons. only "I'm too young to die" modify damage received(halves it).
otherwise you are almost right. a rule of thumb is that a player plays the hardest difficulty setting knowing what awaits him. so if you are playing DooM on ultra-violence or nightmare then you should know where that BFG9000 is, you know you'll need it.

on-topic:
DooM 4 looks amazeballs, I can't wait to put my hands on it. classic DooM had always been about simple and straightforward fun, and DooM 4 looks like will be delivering just that and with a touch of the elements of 3.