London claims to be the kewlest city in the world, and it is quite fun. It's the kind of place that you explore your whole life, and still see something new. The stage shows, bookshops, pubs and clubs are my favourite things in London, as there is always something new to see, read or drink. However, sometimes the city can be a little overwhelming, especially when the weather gets cold and rainy and you have been tramping around in the Underground. London tends to feel a little like a grey wet Disneyland when massive amounts of tourists arrive in the summertime.
Almost everything is expensive, especially food and accomodation.
If you are going to London for the first time, and you only have a few days, I'd visit Westminster Abbey/Houses of Parliament, St Pauls Cathedral, Hampden Court, Soho, Piccadilly Circus, Trafalgar Square and Covent Garden. The musicals and theatre are great, and no trip to London would be complete without seeing at least one show.
The best thing about London is that you can relax and just be yourself, no matter what turns you on. And don't get upset about some of the people who may be a little rude - some of them are just a little uptight, so there is no point worrying about them.