London: ugly or beautiful?

Reading different threads, I've noticed how varied opinions can be regarding London's beauty. Some people call it stunning and some say it's hideous. I just wanted to know what your thoughts were on why opinions on some cities like Paris can be so sure ( I've never heard anyone call Paris ugly) and why opinions about cities like London's aren't. It would be great if you gave your opinion about London, but lets please not turn this into a pissing contest.>