I used to live in London and it has positives and negatives (like any place!)

Positives....

Loads and loads going on, tube/bus can get you everywhere you dont need a car, wages are higher than the rest of the UK

Negatives....

Everyday you wake up and see the colour grey (seriously!!) grey sky/buildings/pavement... it can get depressing, it can be a very lonely city at times, you have to watch your back/wallet/purse/bag most of the time, it's VERY VERY expensive! You will prob only afford to live in a bad area unless you're very rich or very lucky! Bad areas are BAD. Your friends live all over the place and it can be very difficult to get accross London to see them, the noise, the amount of people, the pollution, the tubes (!!).... I could go on for ages!!!

As you see this is biased as I lived in London for two years and moved! I would never go back. BUT I know lots of people who LOVE it! So don't take my word for it, I think everyone should live in London once in their life!