The argument people often make is that it was iconic in earlier revisions, but has become more difficult as the network has been extended¹. If you look at the historical versions², there definitely feels to me like there is a tipping point where it became more challenging to scan.
I believe there is a genuine beauty when you're in the network and have the lovely design on shorter sections(Olympia branch on Piccadilly/District springs to mind), or the simplistic single line vertical maps on the entrance to individual lines.
Having helped tourists navigate the hotspots it becomes clear that the people most in need of a map often aren't helped by the current complexity in parts. Renaming stations might be a nice idea too. Imagine hearing the Covent Garden message if you're a foreign tourist, or British but new to the word alight ;)