I've no idea why, but in my previous time I was in New York I didn't go to subway. Even just to see around. However I really love to wrote about metro in different cities. So fixed it now.

NYC subway is one of the oldest underground systems in the world. First stations were opened in 1904 and look very ascetic. It feels like nothing really changed since the opening (:

The very thing which catches one's eye is the dirt (it's everywhere) and tones of rats on a railway. People don't feel wrong about throwing trash on the way. Rats also feel very comfortable there and even don't hurry to run away from coming train.

Usually it's a bit crowdy in cars. If you're not lucky, you might spend more than 5 minutes waiting for the train. One time I was waiting 15 minutes!
There are different train types: normal trains, slow and stop on every station, and express train, much faster and might skip several stations in a row. One might save a lot of time using a combination of those trains.

Connections are also a pain. Long horrible (in the evening also empty) corridors. If you don't know the way, you might easily get lost. If you accidentally skipped your station and wanna go back, it might be not that easy to catch the train back. On some stations you have to exit and pay for the entrance again to go on the other side. It's 2.75$ for the trip!

In the coldest days local homeless people are going down for the warm. The smell was awful. One day I walked through the entire train (with a hope to find the place without smell), but there was a guy like that in every car. I had no choice but suffer.

From the other side there are musicians and performers who are happy to make you smile for a small fee.

Yet another awful thing in here: subway closes some stations for the weekend. It happens way too often. Thus always double check where and how you go, otherwise you risk going to the closed connection (like I did twice). Also keep an eye on wall prints. It might contains helpful information.
Locals are not happy with subway either. NY times release amazing article based on tweets and facebook posts. Highly recommend to watch it.

PS. On the way to airport aged woman (around 70) started to talk to me. Well, word after word and she's already telling me that she's reading Putin's biography, that he's such a brilliant leader (really?), managed to organize excellent World Cup 2018 (which she visited). She even had a badge with Putin. Then she added that Trump is a newbie in politics, he doesn't understand a bit and is a pure catastrophe for US. Really? How is that? Please tell me somebody decided just to troll me (: