I haven't seen much of it, yet, so I don't know.
It looks like BC will be better; more destrucability; vehicles; more mulitplayer action, but only time will tell!
Check out the gametrailers
video review of CoD4 - I agree with it for the most part, though I'd have scored it less for having no cover system, no co-op play (at all) and the fact that you can't get in or drive any vehicles (other than the odd occasion when you get to man a machine gun from a chopper)
. I'd have given it 8.5 - but please keep in mind I only had a short time with the game!
From what I've seen so far, yes, it looks like it's worth £40.
Phenom