I am pretty sure that the London Underground is the first underground system I have used anywhere in the world. When I first visited London as a child, I thought that it was the best form of public transportation ever invented. In my little world, I perceived it as cheap (50p - keeping in mind I was buying child tickets), 'fast' and 'efficient' (keeping in mind that I often went the same couple of places in central London and didn't have any tight schedule).
Now I find that it is anything but cheap, not as quick as I once remembered and... frequently having problems somewhere. I've probably used the Underground 5-6 days per week in the past month, and it just seems that most of the time, I will see a line closed/partly closed for engineering work, or a station(s) (sometime major, like King's Cross) closed down for some reason (e.g. escalator does not work) and various other issues that can considerably lengthen one's journey (I've had my journey time doubled in more than one instances). Now I am all for them putting the passenger's safety first, but are other, seemingly less problematic underground system I've used elsewhere in the world less safe?
The benefit of living in London still outweigh the negative in my current view. But the London Underground doesn't seem to have improved much in over a decade despite all the disruptive work and price hike. And while I couldn't live without, it's no longer my favourite underground system.