It features NPH on keyboards playing the theme to his hit tv show from his (and ours) youth, Doogie Howser, M.D. The rest of the SNL cast backs him up as his orchestra.
The single tear he cries at the end really makes it.
Neil Patrick Harris seems to really have fun with his image as Doogie Howser. Check out this Old Spice commercial where he introduces himself as a former make-believe doctor… a doctor for pretend.