As far as pure philosophy goes, I would say Mcginn is competent. However, the days are coming to an end where pure philosophy has any legitimacy weighing in on such issues as consciousness and the brain. These are becoming issues to be dealt with by science (neuroscience, cognitive science, psychology) and not armchair philosophy. The mysterian approach that Mcginn adopts is defeatist at the outset. He doesn't even really try to make himself aware of all the work being done in neuro and cognitive science. He starts from first principles, like the philosopher's philosopher that he is. All in all this is good for those swayed by intuitive philosophical arguments but for those of you who actually care to know anything about consciousness, look elsewhere.