Magitek Armor from Final Fantasy 6

Especially during the military base mission

I played this game dozens of times ... and ... I had no idea!!

Great, so you can either extensively practice to not make it useless, or save your time and stick to better weapons. And even then you lose half your health defeating the boss!

I stand by my verdict.

Daedric weapons in Morrowind, they do good damage, but they weigh too much.
Energy weapons in Fallout 2, they often reduce enemies to ashes and unlike what Fallout wikis say, it's not just the annoyance of having to pick up the loot one piece at a time, maybe I don't remember well, but IIRC it often destroyed loot too, maybe this issue was patched unofficially after I finished that game. No problem, anyway, I preferred the Gauss rifle, or even better the faster and almost as deadly Gauss pistol, that gave me the possibility to shoot even twice per turn and have also two or more action points left to reload, retreat at a safer distance or else (but this made avoid destroying the loot of random encounters even more essential, due to scarcity of ammo).

The sword Kratos must use to defeat the final boss in the first God of War, because it's slow, mandatory and the game throws the final boss at you before you can know its moveset.

Shotguns in COD? I love how the pellets disappear into thin air past`10 feet.

The paper fan in Smash Bros. It just felt weak that it's better to hit your opponent without the fan.