Players cannot lose control of their character other than being pushed/pulled, or slowed/immobilized.
Enemies can be stunned, feared, frozen, and interrupted in addition to the above effects.
Sturdy foes and Bosses generally resist these effects.
@Knockback: 
Knocks foes away, while being knocked they do not attempt to attack, unless they were already animating an attack.
@Pull: 
The reverse of Knockback, same rules apply.
@Slow/Immobilize: 
Slows movement by a percentage, immobilization is a slow effect of 100%. 
@Chilled/Frozen:
Technically same as slow and immobilize, only it usually has some additional frost-based mechanics.
@Stun: 
Prevents any actions form being taken and pauses all cooldown timers for the duration of the stun. Repeated stuns have diminishing returns!
@Interrupt: 
Interrupts an attack animation and puts the interrupted ability back on maximum cooldown.
@Fear: 
Causes the enemy to run around erratically, but direct damage may cancel the effect.
@Bleed:
Other than dealing damage, bleed effects also prevent health regeneration of enemies.
@Burn:
Other than dealing damage, Burn from all types of effects will spread between enemies, companions, and players in co-op. They spread once per damage tick to a random target within 1.8 meters. The spread burn only has 80% efficiency and only affects non-burning targets, so it does not refresh nor spread infinitely.