In terms of satsifaction when used:
5) Healing Axe (Team Fortress Quake) - infected enemies with a communicable DOT that could only be healed by a friendly healing axe. An easy way to spread panic and chaos among the ranks
4) Lancer (Gears of War)- Because we don't get a game with a chainsword, a chainsaw bayonet is going to have to do.
3) Gravity Hammer (Halo 2, 3, ODST) - Sure the energy sword is the better weapon in general, it's just the size, AOE and the ragdoll effect make up for it.
2) Sledgehammer (Red Faction: Guerilla) - A hammer that even Thor would envy, the weapon, especially in multiplayer, serves well in the place of a more sterotypical explative when confronting a problem.
1) Katana (Conkers Bad Fur Day) - probably one of the most overpowered weapons in multiplayer game history, the katana could easily lop your opponent in two. If you juxtapose the brutality of the slaughter with the cuddly nature of the games characters, you have a recipe for joy. If there were a reason this tops the list, it's thanks to the CTF game mode. There was just nothing quite like being chased by the opposing team while carrying the flag only to jam the flag down and whip out a Katana, flip out and totally murder your pursers, then picking up the flag and carrying on about your day.