The super shotgun from DOOM 2 remains my favorite FPS weapon of all time.
I just find it perfect. I find the concept of it perfect. It is sort of like a melee weapon, because you have to be literally in front of whatever you're shooting to do maximum damage. But oh my, what damage you do.
Now, normally you'd think that's a huge disadvantage. Most of the monsters are more dangerous up close, if for no other reason that it makes dodging their projectiles much harder. You'd THINK that this means the super shotgun is a bad weapon. But no. AFAIK, there has never been a faster FPS protagonist than the DOOM guy. He has to be running at around 30mph. Because you're so Goddamn fast, using the SS becomes this intricate dance, where you zip into a bad guys face, unload massive damage, and zip away again before he can retaliate.
It's the most satisfying shooting mechanic I can think of. I just love it.