I suggest you play GW1 though this takes place quite some time after the events of EOTN some background probably wouldn't hurt also being that GW1 is an awesome game and free to play..

You will be able to "pick up & play" GW2 with no knowledge of GW1. GW1 players will have "bragging rights" over you as their accomplishments can be placed into the Hall of Monuments (in Eye of the North), but as ANet is *extremely* dedicated to game balance you won't miss out on any game-breaking things. The exact rewards are not known right now, but (given past tendencies) they'll probably be exclusive armor/weapon skins or displayable "heritage" titles. If this is something you can't live without, you'll always be able to buy GW1, link accounts and grind up the old titles for your GW2 character to inherit.

And if you want to get into GW lore without buying GW1, ANet has planned a series of novels to cover the game-world developments between GW1 & GW2.