Mind the gap! Seriously, the tube is an excellent means of getting around London. Their service runs just about anywhere you can imagine in the city. It is clean and on time! I got an Oyster card while in London and its the best way to get around London!

It is an experience. . .the ticket machines aren't the worst to deal with. . .the sheer amount of stops can be daunting, but the Tube is a must if you have any ambition to get anywhere in London. . .solid experience without any delays, problems, or confusion concerning maps. . .

On my visit to London,I found the tube to be reliable,much simpler than NYC for sure,they have great maps,and it is crowded,most of the time.

The coverage of the city is incredible.  You can get within a few blocks of just about every part of the city.  Some of the lines are really slow however, the cars are usually packed, and there seems to be a lot of delays.  But the trains come every few minutes, and like I said, you can get anywhere.