This is the best online game ever made.
You can choose from several classes, including the Warrior, Ranger, Necromancer, Monk, Elementalist and Mesmer. You can later choose a secondary class (or profession as the game says) that can help significantly (for example I am a Necromancer/Monk, which helps me deal out lots of damage whilst healing myself and my party).
The game has a long campaign, complete with cutscenes and voice acting, and it's done surprisingly well and can take you across the whole land of Tyria, on to different islands and caverns, there are a lot of places to explore.
The game can be rather difficult however (sometimes even frustrating), due to the overwhelming amount of enemies in some missions, but this is easily remedied when you find some good team-mates.
The PvP aspect of this game is also great, it's a Red v Blue style game, with people trying to kill eachother as much as possible in different style arenas.
Overall, this game is a truly addictive, immersive and fantastic experience, and should not be missed by any MMORPG gamers, or even anyone for that matter.