let me start by apologizing for not remembering the actual names of these guns.
the gun from fallout 3 that fires 8 nukes with a shotgun like spread, there are no enemies in the game that would require that kind of gun, and there are no situations where such a spread of high damage is needed either.
the gun from dark siders that shoots flaming exploding spears, it may be awesome, but its just so stupid, how can you store remote controlled explosives inside something that is able to be ignited, and how does it keep from going off, it obtained in extreme heat and undergoes big pressure and shocks, first being fired with a small explosion and the coming to an erupt end.
the big biceps in prototype, seriously you can get claws, swords and tentacles of death, and they include "extra strength" and its not like you need extra strength in that game, you can rip building and vehicles apart.
the bees from bioshock, its bees.
the gay ben from the last remnant, its pretty much a nuke you have to set off manually, while your right next to it, and it takes forever to deploy which means you need to have back up capable of holding off an entire army for bout a minute, it pretty much requires that you kill your own army.
the soldier from borderlands's gun, you can not heal bullet wounds with other bullets, its not like a flue-shot.
the gun from pain killer that shoots pieces of wood at least twice as big as the gun, its 20 cm while in the gun but once fired it suddenly grows about a meter or two.
the green goo gun from unreal tournament, its just so freaking weird, its basically the bastard child of jello and C4 with an inbuilt sensor and timer.
the force in any starwars game, basically by level 2 i have more force power than the ones seen in any of the movies (btw how awesome is/where Jedi knight II: Jedi outcast?).