Destruction is often considered to be the 'mage-like' warlock spec; this is based on its more dwarven style of play (fight, drink, fight, drink...). It is true that destruction relies more on direct damage than DoTs or the damage done by minions, but don't be fooled, destro locks are not just emo-mages.
Where the other lock specs focus on shadow magic, destruction primarily makes use of fire spells. Incinerate takes the place of Shadow Bolt as a filler, and Conflagrate and Chaos Bolt are added to the spell book making a dazzling array of... well, destruction.
Destruction locks have the greatest 'burst' potential. This means that they can deliver a high level of DPS very quickly. This makes them ideal for short fights and swapping between multiple targets.
Destro locks are also very mana efficient -- not because they don't get through their mana (they certainly do!) but because they have so much mana restored through Improved Soul Leech.