This week ArenaNet has announced a new class for its upcoming MMO: Guild Wars 2. What distinguishes it from the previous for class reveals (ranger, necromancer, warrior, and elementalist) is that this is a class we have not previously seen in the Guild Wars world.
Now, considering that ArenaNet's talk of this game is that the roles are decentralized, and that there won't be a class dedicated to healing, the fact that this looks and sounds like a tank class are deceiving. However, the abilities present are ones that either benefit the guardian solely, or confer abilities to their teammates.
What manner of skills? Spirit weapons, which aren't a usable weapon, so much as the spirit of one that floats alongside you and attacks, even having a powerful attack that can be used before they expire. Symbols, which can be used to benefit allies or damage enemies. Wards, whose ability I hope is self-explanatory. Then there's Aegis, which is understandably used to block.
This is in addition to their virtues, which are passive benefits. They can become noble martyr types by throwing away that benefit to protect other, more squishy teammates. Or aid them in laying down some smite. Y'know, that sort of thing.
The guardian also seems equally divided between offense and defense. There is a feel from the videos of the skills that while the guardian sounds like a great addition to any team, they are perfectly capable of standing on their own. I'll post my favorite skill I've seen so far below, but feel free to take a gander at the other four on the guardian's own page.