After making his introduction as a sensitive, acoustic-styled songwriter on 2001's Room for Squares, John Mayer steadily widened his approach over the subsequent years, encompassing everything from blues-rock to adult contemporary in the process. Arriving during the tail-end of teen pop's heyday, he crafted pop music for a more discerning audience, spiking his songcraft with jazz chords and literate turns of phrase. The combination proved to be quite popular, as Room for Squares went triple-platinum before its follow-up release, Heavier Things, arrived in September 2003. Mayer...