I've never been an MMO player, but my friend is. He likes WoW and, more recently, Guild Wars 2. The latter doesn't have a subscription fee, so I might pick it up. Is it fun, in your opinions, to play with friends? Can all the quests be done co-operatively?

There are no real quests in Guild wars 2. There are renown hearts, and dynamic events, both of which are just things that happen in the world that you do along with anyone else nearby. The entire game is basically designed to be done with people, but can also be done entirely without people also, except the 6-7 dungeons, those can't be done alone.

There is no need to make parties either, simply being near other people lets everyone contribute to tasks, again, except in dungeons.

And having owned Guild wars 2 since launch, I can say it's a pretty fun game. Although, once you beat it, there's not much to do. However, unless you power game a lot, it should take awhile to finish everything.

The renown hearts really are just your stereotypical mmo quests though. And the dynamic events, while a lot of them are great fun, aren't nearly as dynamic as advertised (though nothing is ever as good as advertised, so that shouldn't surprise anyone).

The game is a lot of fun, but I didn't play it for more than a few weeks. Mostly because I don't like the setting very much, and partly because the character creation options are very limited. If the setting looks interesting to you there's a very good chance you'll enjoy it.

Pretty much this, except I need to add that the game has a pretty high replay value. Every race has a unique section of the storyline as well as each of the orders in the game and some storyline quests even have multiple ways to do them, so there's some room to make playthroughs unique.