I agree that it looks awfully good - certainly better than any of my ISO maps have turned out.

As far as suggestions, there are a couple over/under crossings where it looks like the "over" passage was intentional excavated uphill, straight over the lower passage, and then downhill again. While it's certainly possible that miners (or whoever is doing the excavation) would go to such lengths to avoid an intersection, it does cause me to question why. Given that ISO maps can be highly subjective, it's possible that my brain has just picked the wrong (i.e. not your) interpretation of these crossings - in which case I wouldn't bother making any changes. If you're feeling ambitious and want to change it - I'd recommend trying to keep both passages relatively straight when doing an over/under crossing - or if you have to curve a path, try curving the top passage "down and close" instead of "up and away" - I think it'll make the passage seem more like a legitimate curve than an "up and over" bridge of the lower passage.

Again - I think the map is wonderful as-is - it's just insane rabid perfectionists (like me) who can always find a nit to pick. (None of my maps are ever truly "finished" - I just stop working on them at some point... )