Reger's music is an amalgam of Bachian counterpoint and chromatic Romantic harmony—the result is writing of great density. This is particularly true of the 'Bach' Variations, Reger's piano masterpiece. Hamelin's superb virtuosity allows him to focus purely on the music, so keeping any sense of heaviness from infiltrating piano writing which, in other hands, can sound merely laboured.
The 'Telemann' Variations are much less chromatic, more decorative, and as a result are much closer to the Baroque concept of 'variation'. Their virtuosity is more obvious, with many opportunities for the soloist to display his fingerwork.
The Five Humoresques reveal Reger in lighter mode. Here the inspiration is surely from Brahms.