DISCLAIMER
Everything in this guide may or may not be accurate. The vets above me will most likely have better suggestions. Just saiyan.

For the newbies.
What are superweapons? They're the weapons at the very bottom of the buy menu, along with one on the far right, and mid-left.
They are as follows:
Name (weapon type): cost, clip size, semi/auto
Shock Revolver (Pistol): 8K, 100, semi
Nailgun (SMG): 15K, 200, auto
Railgun (Sniper Rifle): 20K, 50, semi
Seek Rifle (Assault Rifle): 15K, 100, auto
And the "ultimate" weapons are:
Minigun (Machine Gun): 20K, 300, auto
Blast Cannon (Shotgun) 20K, 75, auto

What makes superweapons "super"
Superweapons are characterized as follows:
- Single clip
- A clip of ammo is 1/2 the price of the gun EG one clip of minigun ammo is 25K
- All have special effects, which is as follows:
Shock Revolver: Ignores shield
Nailgun: Bullets pierce, bullets quickly fade.
Seek Rifle: Slower bullets, but "seeks" AKA homes into nearby targets, slow bullet speed.
Railgun: As with all sniper rifles, you see twice as far compared to other guns, extremely fast bullet speed. Enemies are shown much clearer. Halved movement speed.
Minigun: Much like machine guns, does extremely high damage to vehicles. Halved movement speed.
Blast Cannon: Shoots explosive pellets that can shoot things into the air, and can shoot over walls, much like flashbangs and grenades, slow bullet speed.

What to do when you're against a superweapon
Simple, just stay out of their way, and try to waste their ammo, so they won't get enough money to get another clip. Kill them before they can get another clip.

What to do when you have a superweapon
Conserve your ammo, and aim for groups.

Superweapon-specific tips
Shock Revolver: It's basically a 50-clip Desert Eagle. Just try to not be too trigger-happy
Nailgun: Aim for groups in lines, the bullets pierce, use that to your advantage, but make sure to stay close. Bullets fade quickly.
Railgun: Snipe, not much to it.
Minigun: UNLEASH THE BULLET HELL!
Blast Cannon: Unlike the M3 and SPAS, the Blast Cannon's "pellets" can travel a long distance, and has the property of exploding, leading to certain things like Blast Jumping. Also use to completely destroy just about anything.

This thread will need to be updated next version

Btw:
Shock Revolver tip
Not many remember that the Shock Revolver is a pistol, so it can be switched to almost instantly. So one very effective but lesser-used tactic with the Shock Revolver is to simply buy a Shock Revolver and keep it in your inventory, and keep using another weapon as your primary, say MP5. Then when your enemy thinks you're gonna reload, decides to barrier or is in a disadvantageous position such as going up stairs to reach you, switch to Shock Revolver immediately and spam it in his face.

This takes advantage of the fact that people will get used to their enemy using a certain weapon, but if you were to suddenly change weapons and shoot immediately, they will be taken by surprise. And because of Shock Revolver's high DPS, you can kill them before they can react.


Seek Rifle and Snipers note
Seek Rifle currently sees x1.50 the usual range, but will be x1.75 in 0.693 (changelog).
Ruger only sees x1.75 the usual range
PSG and Railgun sees x2.50 the usual range

Railgun's special ability is a subtle ZoomShadow. What it does is, if your enemy is NOT anywhere behind an infinitely tall wall (collision), you can actually see him a lot clearer than usual (he'll appear more opaque) regardless of height (normally its harder for you see someone from a different height). This is a subtle but useful advantage for any sniper.

Nailgun:
For Use in:
Crowd Control
Why:
Bullets pierce through more than one person.

Railgun:
For Use in:
Sniping/Support
Why: Basically one shot kill, You can view players more clearly, Which allows you to get to more strategic places to snipe.

Seek Rifle:
For Use in:
People who suck at aim, Countering BT (In some cases), and Med-Far range combat.
Why: Bullets seek, Even in BT. The seek can really help in Med-Far range combat.

Shock Revolver:
For Use in:
Rape
Why: As stated in STMs post, It can quickly be drawn out and blasted into your opponents face, Ontop of that, It goes through barrier.

Minigun:
For Use In:
Crowd Control, Destroying Vehicles
Why: High DPS can shred through crowds. It also has a damage boost towards cars, Tearing through a pickup in a couple seconds.

Blast Cannon:
For Use in:
Movement, Rape, Smoking out.
Why: Blast jumping. High Damage, Especially when paired up with Crit Shot. Allows you to lob bullets over boxes to prevent people from regaining health/mana from a defensive point(A box, A small wall, Etc).

:O
Shock/Blast are now officially NSFW.
On-topic: Curses STM, you're right ._.
But then again...

Garde, what is with the ten vamp nub for your signature?

Because... I'm a 10 vamp nub.
On-topic:
There is a distinct lack of traffic here.
Also, I forgot to mention (even though other people did)
Shock Revolver is a PISTOL, which means an instant draw time. Use it to cause massive amounts of pain... All while making people realize that their shields do nothing but getting them killed.

10 vamp nub

I see