I've just returned from living abroad in London for a year, and being home (Miami) is drastically increasing my insanity levels. The cities just can't compare.

Best things about London:
Taking a picnic to Regents Park on a nice day.
Walking around Camden markets and finding random things you don't need but all of a sudden you think you do.
Going to a pub and meeting random people and chatting away all night.
Getting cheap tickets departing from Luton/Gatwick/Stansted Airport to go visit other amazing places.
Getting anywhere by an impeccable public transportation system.
Free stuff. There's always something free to do.
Portabello Road Market. Always interesting to walk through, even when you have no money to buy things (as often was the case for myself).
So these are some of the things I am going to miss about London, as well as just the happiness of my life there.
Good thing I'm returning in a few months!