The level of detail is quite amazing, and the story is quite interesting, particularly to understand the subway in connection to the city (like how transportation hubs emerged, other trials like the vacuum train, etc.). The tour spends quite some time above ground, but there's really a lot of explaining to do, and it's a pity that the actual City Hall station is closed for visits. Plus, the New York subway is so incredibly noisy (more modern systems are way quieter) that it's difficult to follow the guide when in the station. It one could ask for the moon, I'd suggest using headphones for that part of the tour. Other than that, it was very nice!
Plus Justin was a super engaged person who stayed talking with us after the tour, and walked some of us to town afterwards. These little things also make a great difference!