TfL make a great job of running a vast underground network, carrying millions of passengers a year safely and pretty much efficiently, over parts of the network where (the tunnels at least) date back to the early days of steam.
That is before you add in the ‘overground’ network that also falls within TfL’s orbit.
There is a huge difference between the lines, the Northern Line trains being physically much smaller than the modern trains found on, say, the Circle, District and Jubilee Lines. Likewise, the stations are different, often telling their own architectural story or mapping the growth of London outwards to the suburbs.
We (London plc) are very lucky to have such a good and pretty much well functioning public transport system. No question about it.