As per the title. Trap setting (and crafting!) should be featured in this game, with a variety of traps, each having different trigger mechanisms and effects. Clearly some classes would be better suited for trapping than others (Rogues/Rangers) Some not so exhaustive lists for example:
Motion Trigger: Trap triggers when hostile moves within X range of trap.
Tripwire Trigger: Trap triggers when trip wire of extending X feet from trap is moved over.
Manual Trigger: User triggers trap manually.
Delay Trigger: Trap automatically triggers after a delay of X seconds.
Magic Trigger: Triggers when trap senses magic in a radius of X feet around it.
Sound Trigger: Triggers when trap senses sound in a radius of X feet around it.
Visual Trigger: Triggers when trap spots hostile.
Sentry Trap: Locks onto and attacks tripping enemies. Can be equipped with ammo and weapon of player's choice.
Gas Trap: Releases a poisonous/acidic gas.
Snare/Net Traps: Immobilizes/slows a tripping enemy.
Explosive Trap: Detonates when tripped on hostile.
Jet Trap: Discharges a jet of X damage type when tripped. May have secondary effects (in the case of poison for example).
Blade/Spike Trap: Swirling/pulsing stationary blade/spike trap.
Spell Trap: Casts X spell on hostile when triggered.
Alarm Trap: Makes a loud noise and highlights triggering hostiles with paint/glitter, etc...
Stunning Trap: Stuns and disorientates enemies when tripped.
Trigger and trap types could be mixed and matched. For example, a delay trigger could supplement a proximity trigger, the trap going off 5 seconds after the proximity trigger was tripped, in turn activating a joint Stun and Sentry Trap that fires on consequently stunned foes. Crafting would occur by joining separately purchased modules together. Setting traps would either utilize an existing skill (such as Disable Device), or a new one. The result of the trap setting check would determine the difficulty of enemies spotting/finding/disarming it, in addition to any innate modifier of the trap itself. Critical trap setting failures causes the trap to backfire.