"Open world" is one of those nebulous terms that means a lot of things to a lot of different people.
The extra-credits pieces describes Baldur's Gate as a open world game and I guess it technically is; there are lots of locations one can go to, you can keep going back and forth to them and if you don't touch the map button you can walk between most of them on the "normal screen" (much like Fallout). But does anyone really think of it as an "open world" game? It's basically a number of completely separate maps that you can travel back and forth to but are largely separated and I doubt there's many (if any) people who actually traveled between all the various hubs without using the fast-travel option... put simply there was nothing there to keep the player interested.
And that's the issue that confronts open world games. How do you make traveling through the open world interesting?
My own preference is generally the skip the "open world" aspect in favour of having specific well-crafted and often fairly large individual areas; Baldur's Gate, Fallout or Arcanum are the classic examples of this but one could also look to either of the Witcher games or the first Dragon Age for pretty good examples. Hell, even Dragon Age 2 to an extent (although the less reused warehouses/caves the better). That said there are some elements of the open world that do work.
I'm not great fan of the more recent Bethesda games but, as much as it's used as a disparaging term, the "hiking simulator" aspect of it is arguably the best part of the game; there is undoubtedly something rewarding about finding shortcuts up mountains, seeing a location pop up on your HUD and getting there or simply going for a walk and seeing what happens; more than once when I've got 20 minutes free or so I'll pop in Skyrim, load a game, give my destination and simply walk there.
Inquisition sits in a fairly awkward position in that it's sort of open-world and sort of not. It's not a full open-world in the way Skyrim is but the areas are large enough that they touch on being open world. And not always particularly well. I hate to pick on the Hinterlands again but it's the best example; it's a huge area and thus Bioware were confronted with how to fill it. And their decision was endless MMO-like fetch and collect quests. And that's not a good way to do it. Skyrim had its "radiant quests" but I don't think anyone particularly liked or enjoyed them; they were something people did because they could rather than something you were hit over the head with.
It's arguably my biggest concern about the Witcher 3. Both the Witcher 1 and 2 featured well, crafted, engaging large areas which functioned as hubs and were actually fairly linear (one generally couldn't travel back and forth between all of them at a given moment). If the open world aspect of the third simply gives a way to travel between such hubs without using fast travel but without putting much content in there then what's the point? And thus they have to fill it with content... but find a way to do it that isn't just repetitive fetch/kill/collect quests.