I was too much concerned during my working life with things such as safety (not specifically airlines mind you), that I understood the importance of safety briefings. That said, and as a couple of other posters have pointed out, there is a difference between the message and how it's delivered. I'm convinced that there's more chance of the message being taken in if it were half as long (or even less). Furthermore the briefing would probably benefit from serious cuts, with everything that isn't related to emergencies being removed. Too much information will simply mean that nothing is assimilated (just listen to the verbal diarrhoea from politicians as an example!)
I still remember when the briefing was done by video and I was supposed to be impressed with the message being delivered by personalities I'd never heard of. I found it neither funny, nor informative. I don't live in the UK and it largely meant nothing to me. Just watch the Qantas briefings which were along the same lines and were even more meaningless.