Returning player, completely mindblown!
For that sort of thing the profession specific forums would be better.
Well, Halloween starts tomorrow, so I’d say that’s a pretty cool place to start. Every two weeks there’s a new Living World release that lasts for 2-4 weeks or so, and while you’re probably not going to love every single one of them, they do generally provide a lot of stuff to do if you’re looking for new content.
There’s always World Completion if you feel like exploring the world without raising alts.
I’m not an expert on builds, much less Guardian builds, but, as Khisanth said, you can probably get good advice from the Guardian forum.
From a related thread (here, for attribution). Two videos you might want to watch. Good background information on how the game has changed.
http://www.youtube.com/watch?v=Ce_dvXJercI
http://www.youtube.com/watch?v=eUfV3OBLyc8