From what I saw with Fallout 3 is that they are at least bringing choices back into the equation. And I remember the entire world being literally open this time. Might be wrong.
What still concerns me are the guilds and the skills.
They really need to turn it back into a place to find work, and not just a story in which you are elected to save the guild. As in, quests available at every guild hall, not one at a time. I think the storyline (if there is one) and the jobs should be separate but reference each other at times.
As for skills, there need to be more, of course. But the skills you choose should actually dramatically change the experience. As in, I can solve most quests with violence, stealing, or persuasion.
Random monsters/animals in the wilderness and especially in caves should be much fewer in number and easier to kill. The bigger battles should be even bigger and more dramatic but also fewer and the majority I should be able to talk my way out of/ avoid altogether with stealth.
And no battles (except maybe the final boss) should lock me in a little room until I'm finished.
This way almost every dungeon-crawl quest is suitable for the fighters who want to hack their way through, the thieves who want to sneak past everything, grab the target and teleport out/ escape, and the diplomat who wants to disguise/ sneak his way to the target then bribe or persuade.