I don't know if you've lived there or not, but I'm going to assume you haven't and give you my experience over 3 years.

1) Public transport is good, when it works. It often doesn't.

2) Public transport is good, until you have a job that has structured hours- which is most jobs, as evidenced by the INSANE rush hour. 20 minutes in some guys armpit feels like multiple hours.

3) You can't afford to live somewhere nice. I mean, I earned quite a bit more than the average and was spending 50-60% of my take home salary on rent. And I lived in a bad neighbourhood. (because I wanted to live alone).

4) Pubs have the same problem as the transport system, super crowded at rush times.. spills into the streets, especially in the west end/theatreland.

That said, if I had the money to live well in London, it would be a great place to live.