Since everybody else seem to be commenting on the newly opened Copenhagen metro, I might as well give my eurocents worth of comments:
To me as an individual the Metro is useless. There are no stations near where I live, nor does it run on any route that I'd regularly travel. Furthermore there are no plans to expand the Metro-net to my neighbourhood. So yes, I probably am biased when looking at the Metro as a whole.
To me as a citizen of Copenhagen the Metro seems like a waste of money. With it's very limited amount of stops it accomodates a select few of the people in the city - too few to justify a train every third minute. The Metro may turn out to be a great addition to he city, if the "Cityring" is established. The Metro people estimate this to happen not until at least 2010. With their trackrecord of estimating we're looking at a cityring and subsequent usable Metro in 2020. That's if it happens at all, and that's a pretty big if.