I notice a heck of a lot of activity in the "New Unique Items" Thread, but shouldn't we focus on the 31 that we already have?
Since we're in the Beta phase of 0.9.9, why not try and rebalance/improve the current set of uniques, rather then add new ones?
This is what I think that a unique should be:
Something that makes it stand out from the class it belongs too (Armour, Melee, Boots, Pistol, Shotgun, Rocket, Rapidfire, Power). This can be either being more powerful (Damage, Accuracy, Speed, ect.) Or having a distinguishing trait (Regeneration of ammo, Multi-use Nuke, Different firing system (Think Assault shotgun vs Combat), ect.).
Uniques should be better then the basic weapons in their class, but do not need to be overpowered. That said, If a Unique is "powerful" It should have a drawback(s).
In addition, All uniques should be useful in their particular class. (See: BFG10K. It's not useful.)
Go ahead.