Take everything you know about wow... and then throw it out the window. This game has no factions, no raids, no constant gear grind, no ganking, no mob stealing, no static combat, no sub fee, no racial advantages to playing a certain class, no spell rotations, no flight paths, no running back and forth to npc for questing, and tons of other differences.
And for the record, these are all good things. The GW2 beta was the most fun I had playing a video game in years. About every 15 minutes I would find something I didn't know about and say, "My god, why haven't games been doing this FOREVER?!!"