Guild Wars 2 developer Jon Peters just posted some interesting information on specific gameplay systems that players will use in the game, including an exciting description of Guild Wars 2's combo system and a good explanation of how pets will work.
Combos work by having one character, the Initiator, create an area of effect that modifies actions performed within it. The second character, the Finisher, then performs and action that takes on new properties within the area of effect. As anyone who had played Magicka could have told them, ArenaNet discovered that stacking combinations was "incredibly overpowered."
Peters uses an example where one character might create a Firewall, and another uses Ricochet through the flames to get a bouncing axe that burns targets. This seems like a neat idea, and something that will be really satisfying to use with a regular party.
Peters also explains that pets are now defined by their species and family. The two classifications determine what a given creature can do.
"Each family has three basic skills that define that family. For example, bears are hard to kill, drakes do AoE damage, devourers use ranged attacks, etc," Peters explains. "These skills are automatically used by the pet. Each species within a family has a unique skill. For example, polar bears have an icy roar that freezes enemies, while brown bears have a roar that removes conditions."
I don't like playing with pets because I find them adorable, and suffer from guilt and depression when they die. The last pet I had was the badger in Neverwinter Nights. Let's not even discuss Dogmeat.
But maybe you're okay with with cold-blooded, make-believe animal exploitation! If so, you will be able to use every type of pet in the game. All rangers need to do is find and charm each species. "In Guild Wars 2, a single ranger can collect and use every type of pet in the game without having to worry about stables or leveling the pets from scratch," Peters says. So exploit away.
There is a lot of other great information on the blog if you want an idea of how these characters will actually play. But I cannot tell you any more. I draw the line somewhere before talking about specific keyboard bindings.