If you want to drill down a bit you're going to have a hard time knowing where to start. We've got the addition of the fishing hobby, and the awesome new fishing trophies for housing. The LFF and group questing mechanisms have been improved, and monster players have the all-new Orc Defiler to look forward to. For some of this news straight from the source, make sure to check out our interview with Jeffrey Steefel from back at the end of March. And If none of that is enough, you can also read through the official patch notes. They'll keep you busy for a good, long time.
If you're still not satisfied, take a breath. Don't worry ... Book 14 is already on the way.