Well, (as I said the FIRST time I suggested the super shotgun idea) I made it to fill two niches:
Inefficient but effective shotgun (For two shells, 9d4 is pretty lousy damage)
A double-shotgun based special weapon (Jackhammer, Assault and Plasma Shotgun are all based off the Combat Shotgun)
The current "Double Shotgun" is nothing like DooM 2's "Super Shotgun" anyway, hence the name.
The double shotgun of DoomRL's main drawback is that it has a long fire time in which you must stand still like a moron, whereas in DooM 2 (and with this exotic weapon) the fire time is absolutely nothing, but it does less damage to compensate.
I think the Super Shotgun is a good idea, but we really need more Melee exotics, and this is coming from someone who doesn't care about Melee.
...really? We already have 3 if you include the chainsaw.
Besides, it's hard to make melee interesting. The only two melee weapons I can think of that would actually force you to change the way you fight are:
Plasma SwordExotic WeaponInventory Description: You need a description? It's a SWORD made out of PLASMA. Duh.
Damage: 9d9
DamageType: Normal
Accuracy: +1
Clip: 100 plasma cells (Attacks cost 15 cells)
FireSpeed: 1.0s
ReloadSpeed: 2.0s
Altfire: Costs all 100 cells. Slashes out an energy wave that damages all enemies in a line, like the railgun. Counts as a melee attack for most intents and purposes, but does not get a damage bonus from berserking.
Unholy ScytheUnique WeaponInventory Description: Killing stuff is easy, it's getting back in to combat position that's hard!
Damage: 13d6
DamageType: Normal
Accuracy: 0
Clip: N/A
FireSpeed: 2.0s
ReloadSpeed: N/A
Altfire: Smacks someone with the blunt end of the scythe. Does half damage, but only takes 1.5 seconds.
PRE-POST EDIT:
Cobalt raises another good point. The LS is already the end-game weapon of choice, so these weapons are balanced to be better than the LS... but only in some situations.