What I want out of the next expac, as far as open world PvE is concerned: meta events with replayability value on the one hand, and exploration that's fun on the other. I want some maps that have a mapwide meta with mechanics that require a bit of coordination, like Auric Basin or Tangled Depths. That would be the part where I go for action, loot, and organised gameplay. But I also want zones where I can stop and find cool stuff without being f-ed over by random mobs or environmental effects every time I look away for five seconds. Somewhere along the lines of Grothmar Valley, which I love because it took a step back from the ridiculous "let's just put damage over time effects on half of the map and a bunch of trash enemies ganging up on you on the other, so you can't get from A to B or explore that funny looking tower." All the NPC conversations and random tidbits that you can actually stop and listen to add greatly to immersion, in my opinion.