As I only play it on an xbox that cannot be connected to the internet, I'll not be able to answer that one for you. I've played the single player for 3 2-hour sessions on hardened Mode and I've nearly completed it. As good as the story line is and all the cool things you can do, unless you're going to spend hours upon hours on online multiplayer, I would not say that it was worth £30.
With BF3, however, the single player is poop (although graphically astonishing). It's the multiplayer with is worth more than they charge. Think BF2 with all the best bit of BF:BC2 thrown in.