A satisfying weapon doesn't have anything to do with reload speed, or power (just a little bit, explained) or ammo or something like that to me.
It has to do with the effect it has on enemies. The nail thingy in FEAR is AWESOME! Nothing short of that. It nails people to walls. How can a weapon be any more awesome than that?
Rail guns are often satisfying to use as well. Large beam and often killing in one hit. And they usually sound nice and have a lot of moving parts that just do things (cool reload). I mean, just check the reload animations of the rail guns in Renegade and tell me those aren't awesome weapons. That game also has a few other awesome weapons. Electricity rifles are awesome, depsite the fact that they don't look very satisfying when you hit people with them in that game. A minigun that sets people on fire (laser minigun) can't be wrong. And the tiberium-guns. Those are plain awesome, I mean, depleted uranium shells, that's quite cool, but shooting someone with poisionous slugs that drain the body of minerals and causes the hit persons to turn into monsters? That's sweet...
Desert eagles and shotguns are often quite satisfying as well. They sound nice, and people go flying backwards. The aurora alpha bomber in generals deserves a mention as well, sure, it's not quite the kind of weapon people are talking about, but damn, when I blow up a whole base with those things I can't even sit down in my chair and lauch like hell. Those are awesome.