5.The Questing System
The questing system in WOW, while greatly improved since the last expansion, is they very definition of the term 'grinding'. Get quest from quest-giver, kill 10 monsters, return to quest-giver for your reward. Rinse and repeat. In Guild Wars 2, while your character's personal storyline might contain a few of these, quests and rewards are often generated by 'events' that are constantly occurring throughout the world of Tyria. Add this to a plethora of non-player characters scattered about who are constantly in need of assistance and players will rarely find themselves lost or without something to do close by.
6. No Monthly Subscription Fees
Did I mention that Guild Wars 2 has no monthly subscription fees?