I played the E3 demo and was hooked all the way until the test sadly ended.
Admittedly, I mostly played the PvP scenarios they had, instead of the quests. One of them was a tournament-style bracket that had various different scenarios, like King of the Hill, Capture the Flag, Team Deathmatch, and Assault/Defend variants. Each tier pitted you against other teams in the bracket and it got progressively more and more challenging. Extremely fun and I was surprised as to how balanced it all was and how well it scaled along with the regular dungeon-exploring mode. It was kind of like a fantasy MMORPG Team Fortress Classic. Really hectic.
I also like how they're handling the skill system so that even new or less experienced players have a chance to compete against some of the stronger ones. Definately looking into buying it later, but not too sure about all those expansions yet.