But there IS plenty of non-main quest stuff even in EA. So there is a ton of exploration.
Main Quest = Save Halsin from Gobbos and take out leaders, OR kill everyone else.
Side Quest Exploration = Tollhouse, Waukeens Rest, Gothyanki, Hag, Bog, Kahga Quest, Spider Lair, Ogres, Owlbear, discovering what happened to the Harpers, the entire Underdark, even the first dungeons isn't necessary but is a part of exploration.
And there WILL be so much more once out of EA. At least, that's how they're setting it up. So I don't get why everyone is saying there isn't enough exploration. The whole dang EA map is exploration with the ability to run right to the end if you want. Right?
It seems it's mostly quest-related, though; I suspect most of the bits in question will be at least tangentially related to the MQ, and if not that then part of another significant side-quest. I'm thinking of just random interesting stuff that one might happen upon that's really not at all relevant to anything and just exists for its own sake. Maybe to add some flavour or background or maybe just because. I guess I just like trivialities and randomness.
