I caught the new section of Delhi Metro on its first day of public operations. It's really world class "an amazing feat and achievement by Indian standards" though whether it will be able to match the demand I really wonder.
They say that almost 3 lakh commuters (almost all of them like me, there for the fun of it) used the trains on the first day itself and boy it was a mess at most of the ticket counters and inside the trains. At least at first glance, it seems to me that a Metro at this scale would not work for Mumbai, probably something on similar lines but at a much grander scale would be needed to cater Mumbai. However, it may just do the job is some quieter parts of Mumbai (i.e. if such places still exist).
But whatever said, parts of the Metro reminded me of scenes from 'The Matrix' and almost the entire journey seemed like a dejavu of my trips in the London tubes.
Please note you are NOT allowed to click photos in/of the Delhi Metro and you could get caught as there are lots of surveillance cameras everywhere and will have to face serious consequences (as I eventually did, but to my luck by some small time security guy who just warned me).