What in your view are some of the all time coolest weapons in gaming, and what makes them the best in your opinion?

The gravity gun.

HL2 death match was great fun, picking up anything and shooting it at others. Toilet bowls, kitchen sink, everything was ammo :)

Gravity gun was the first thing that came to mind lol. But in this case, the Lancer!

A machine gun with a chainsaw?! What’s not to love??? Lol

Zone of the Enders 2's Vector Cannon:
https://youtu.be/t1nrjRFFmpI

It put a wiiide smile on my face back in the day.

As a kid it used to be Metal Gear Rex or something like it, as an adult I find myself impressed more by Astrobots arsenal or Rachet and Clank guns.

Another great one is the Shrink Ray from Duke Nukem 3D, here at 4:12


Tons of fun in multiplayer. With a direct hit you get shrunk for 30 seconds or so and have to avoid the person that shrunk you trying to stomp on you. Your perspective changes to that of a mouse and you see this giant foot coming at you while the other player frantically tries to squish a mouse running around.


Ratchet and Clank carried the torch for inventive cool weapons later on, lot of fun ones. 
https://www.gamespot.com/gallery/ratchet-clank-best-weapons-of-all-time/2900-4437/#9
Fully agree with the list
The Zurkon family, Groovitron, RYNO, Sheepinator, Pixelizer, Suck Cannon are all great.


In Unreal Tournament my favorite was the Flak Cannon, so satisfying to use

Laptop gun from Perfect Dark and the Lancer from Gears.

Buster Sword
Daedric weapons
Golden Gun in Goldeneye
The Ryno from R&C
Plasma cutter from DS
Blades of Chaos and Leviathan Axe
Energy Sword
Gravity Gun
Moonlight Greatsword in every Fromsoft game, but most notably in Elden Ring
The BFG
Blue turtle shell

Lowkey some very weirdly designed FF weapons look quite nice


As for the why, I dunno, depends on the weapon, some are just very destructive that its cool to use them, some because they try (and succeed) in looking edgy and badass and others because they have a very unique style/aesthetic that makes them stand out.

Strider Hiryu Cypher. A plasma sword that can freeze enemies. Burn them. Anti-gravity and more. All wielded so fast it leaves a blur.

Warhammer 40K Chainsword. 

Gears Lancer. An assault rifle with a chainsaw. Need I say more?

The Monando. A laser sword has many abilities, but it can also tell the future. So, any enemy attack gives you a warning to dodge and counter.

The Wiener Whacker, a bwananarang for Donkey Kong from Mario+Rabbids: Kingdom Battle. That's a mouthful.