I'll admit that I only rode the trains a handful of times over five days, but in that time I experienced no delays or service changes (the likes of which are are now all too common in New York City.)
What's more, the language barrier caused no issues whatsoever — something that any foreign visitor to New York would likely say is a big headache for figuring out the complicated system.
All things considered, Mexico City's metro gets a full 10 of 10 rating in my book.