I always enjoy Dennett. Although this one wasn't a good as some of the others I've seen, it's important to remember that the content of a public lecture -- particularly if there is no guarantee of the background of the audience -- needs to be much different than the precis of a book. And the presentation needs be different, also.
I'm not surprised that his ideas meet resistance. Thousands of years of "what is obviously true" aren't overcome easily, no matter how logical or correct the arguments are.
An important point -- which is where Dennett started -- is that a sensible analysis of determinism and free will is required to have any chance of having a rational criminal justice system. To argue for one viewpoint or the other without addressing that concern is to miss the point of why it even matters.
Yes, law would be pointless without free will. Actually, it's only purpose would be to justify the punishment of violators. Intent and guilt would be removed from law, leaving only consequence and punishment: rehabilitation would also be pointless without free will. The fact that laws can work as well as they do provides empirical evidence for the human capacity for free will. Laws are causal factors that influence our choices and usually carry more weight than our individual plans for the future. But sometimes we choose, with eyes wide open, to violate the law if the reward is deemed worth the risk. We do this when speeding or cheating on our taxes or robbing a bank. We know we are responsible for our actions.
I do enjoy reading Dennett much more than listening to him. He speaks haltingly and less eloquently than, say, Sam Harris or Christopher Hitchens. If you've ever watched the Four Horsemen (Dawkins, Dennett, Harris, Hitchens) videos from YouTube, you can observe the difference directly.