Mike Skinner, A.K.A. the Streets, has made the unlikely genre of British rap seem essential — a neat trick, since his "flow" hardly dazzles like Jay-Z's. But with working-bloke wit and a love of simple hooks, he's made magic on records about stoned clubbing, failed courtships, petty crime and pop stardom. On his fourth set, he addresses loftier themes — religion, mortality, ecology ...