A tease of a line. When it works, it's a joy (assuming you wanted to go from Brixton to King's Cross in no time at all). But then you have to deal with the shutdowns, random changes of destination (you wanted to go to Walthamstow? Tough. Make do with Seven Sisters), and the dreaded "being held to regulate the service". Also: noisier than Black Sabbath and Metallica having a semtex fight. But we still love it.
(UPDATE: The Victoria Line was temporarily demoted to 13th place on this list, as approximately three hours after the article was published, some people at Victoria decided to pour fast-setting concrete into their own signal room, almost entirely shutting the line down for the day. It was still better than the cable car, though. It has now been restored to 3rd place, as it is no longer full of concrete.)