By the way, it has come to my attention (don't ask me how, I have eyes and ears everywhere, it actually gets quite awkward) that some people didn't understand what 40oz meant earlier by some maps being "A journey from point a to b to c" and some being "one big point A". I think I understood that sufficiently, so allow me to clarify, please - at least what I thought he meant when I was agreeing with him.
I think the second variant is the sort of totally interconnected maps that you constantly run through in all directions, slowly opening them up more and more and aquiring keys and such. In the end no matter how many "distinct setpieces" or "varying environment types" they have, they feel like this one big sandbox (not in the genre of maps sort of meaning), one big set which was crafted precisely for the player, one big place, call it like you want. Often they don't feel like there's anything beyond their boundaries in the game world. The "Journey" maps, as I understand, are such maps where the progression between the "points" is somewhat linear and you only make the "A->B" and "B->C" trek once, only in one direction, don't have a reason to return to the previous "points", and the places are far and distinct enough that they feel like separate areas between which you have to traverse. I guess if you get technical (or pedantic), the main distinction is the lack of the nigh absolute interconnectivity and desire to cramp the whole layout into some rectangular shape like the original maps were, and a bit of absolute linearity in the global progression. Because technically even about the most interconnected maps you can say that a lot of their areas you only go through once and in one direction... But I hope the point is more understandable now.
As an example, let's say we have a map about some techbase structure and surrounding caves and cliffs. The player runs around this area to and fro, but you would still think of the whole place as "that base". Maybe the exit door was locked but very close to the start, in which case even if you had to traverse the entire techbase for the key it still doesn't end up feeling like a journey, but rather like a continuous stumble in this random, completely outlandishly structured building (and surroundings). On the other hand, we might have a map that has two completely separate techbases, which are connected by, say, a long canyon, with caves, maybe some fields, a swamp, a wooded area, a river or whatnot. But this connection part is at least as long to complete as each of the bases, and obviously you can't see one of them from the other. The player can run around the first one for a bit, maybe to find a key which opens the exit from it, THEN get through the sufficiently long trek to the second base, and THEN either end the level before entering that one or maybe spend some time searching for a key to the entrance and then whatever objective he needed to complete in that second base.
I know that the "one big point A" maps were pretty much all the original Dooms had, but even in this case I think I much prefer the "journey" ones, or at least when there's a healthy dose of them in a set, like at least every third or second one. Funnily enough, MAP01 almost seems like a "journey" map, and MAP02 is quite clearly a "one big point" map. MAP29 also could be viewed as more of a "Journey" map.