I was on a trip to London recently and it was my first time regularly using a public subway/train system to get around. I've always driven before that. How does London's system compare to NYC? I thought London's was pretty good.
London has 2 kinds of subway - the deep tube and the "sub-surface" lines. The deep lines are quite particular to London; narrow tunnels because the technology was new, so the trains and platforms are too small. 5 out of the 7 deep lines run 24h on Friday/Saturday night. Otherwise it's closed between about 1am and 5am for maintenance. Over the last 20 years, they've caught-up on a lot of deferred maintenance. It's pretty rare now for a train to break down or be delayed by faulty signals. They work about as well as they can get them without rebuilding the whole thing.
The sub-surface lines are much more similar to the NYC system. Just below street level, large trains, often only with stair access. Some stations feel very much like an NYC subway station. Mile End for example:
These lines were, until about 20 years ago, in a rather shabby state. Not as bad as NYC, but old trains, worn-out track, 100 year-old signalling in places, unreliable service. They've since
replaced the entire fleet, repaired/replaced all the bad track and they're half way through modernising the signalling which will allow a ~30% increase in train frequency while also being far more reliable.
I last used the NY subway in anger about 10 years ago, and it felt like the shabbier parts of the sub-surface lines, but that was in the touristy parts of Manhattan. Definitely dirtier than London; stations and trains. I imagine the more neglected parts of the network were even worse. The major differences with the London system are continuous 24/7 operation and that many lines are quad-tracked, allowing local and express services. Only two routes in London have this kind of parallel service (District/Picadilly in West and Metropolitan/Jubilee in the North-West).
There are definite parallels between the two systems - similar age, size, usage, and historical neglect due to declining population in the 80s followed by overloading as population rebounded. It's just that London spent the last 20 years or so spending billions on bringing it up to a modern standard.