not sure if that's a good thing, though. it lacks (except in a few spots, like the man of fire midboss fight) the same thoughtfulness of area design that permeated mgs2 and 3 in favor of the open world structure.
I disagree with this. I mean, the area between bases is pretty much nothing, but the actual bases have some really interesting designs in terms of open and confined space, verticality and geometry. I think the main difference is the philosophy towards enemies. MGS 2 and 3, like most stealth games, has enemy behaviors that are very carefully considered puzzle challenges that take into account a single entry point and a single exit point. Since MGSV levels are more open, you don't have that, but I actually think that is a strength rather than a weakness, or, at least, it's why I enjoyed the game so much. It's much less a game about solving the puzzle of how to get by patrol patterns, and more of a game of making general plans and reacting to changing conditions. It's messier, which means I actually made use of more of the mechanics of the game, since clean stealth games tend to encourage you to ignore most of the mechanics in favor of pure navigation. As I said before, I think the main thing missing was larger areas.
That being said, I would love to be able to play on Big Shell with the MGSV mechanics.