Cold, wet and windy. If you go to the main shopping areas, average speed is about 0.5 mph on the pavement [sidewalk], it's even slower on the roads.
Hehe. It's not all bad - plenty to go and see and do. Plenty of decent shopping. Plenty of food to cater for all tastes - expensive haute cuisine, Italian, French, Japanese, Indian, Chinese, Turkish. Plenty of pubs, clubs and wine bars. Plenty of excellent theatre and opera. Plenty of historic sites - 'Buck house', Westminster, St Paul's, many many more. Plenty of art - the national gallery, tate modern. Museums - British Museum, Imperial War museum, Natural history museum, Science museum.
You won't be short of things to go and see or do. And the weather isn't that bad... all the time.