Worked down there for 5 years, overall it was ok.
I loved the weekends, there was so much to do whether you had money or were skint. You have so much choice of where to go out, you weren't stuck with just going to town, you could go to Camden, Angel, Crouch End, Hoxton and many other places to go. I miss the sport as well down there, teams were more organised and sociable. If you were skint there was loads to do with a lot of the museums being free, the parks are amazingly clean and there's many other sites to see.
I do however genuinely believe the standard of living down there isn't as good as it is in Manchester/ the North. The tube is an amazing piece of engineering and so handy, it's easily taken for granted, being able to head in to central London within 12 minutes from a Zone 3/4 area is just incredible. However during the week I fucking hated it, just the glumness and how over crowded the tube network is. If the tube was down then everybody was fucked, there was no alternatives you are stuck. I felt like I didn't have much of a life during the week in London as getting home tended to be a ballache on top of working late. As we mostly drive in Manchester I feel I have so much more freedom and time off in the week. I felt quite limited in London, roads are just angry and congested and everything in generally over crowded whether it's the gym or supermarkets, I felt like I'd taken a hit on the standard of life.
It is an amazing city packed with culture and history with amazing people, I'd recommend the move to anybody, but for me 5 years was enough, fair play to anybody who sticks it out longer down there.