Gigantic city with lots of history/culture and lots to do
What can I say? London is London: a city with lots of history and culture to explore, and lots of things to fit everyone's interests. It can be really expensive, but you can always find deals on tours, lodging, etc. It is a very large city and can take some time to get around, but it is absolutely full of things to see and experience.
Insider Tip:A lot of the museums are free and showcase world history, culture, and art (British Museum, National Gallery, etc.). Also, getting an Oyster Card makes it very easy to get around the city via Tube or bus and can be more cost effective than Travelcards, depending on how long you're in London and how much you'll travel around in the city.