John Denver’s music was considered to be more-or-less middle-of-the-road if not downright conservative in the wake of rising stars like Janis Joplin and Jimi Hendrix.This issue is confronted early in this latest jukebox boomer music revival “Almost Heaven- John Denver’s America” at The Theatre at the Center in Munster, Indiana (only 35 minutes from downtown Chicago).The popular singer songwriter eventually emerged as the nascent voice of the environmental movement with songs like “Calypso” as well as “Rocky Mountain High,” “Take Me Home, Country Roads,” “Wild Montana Skies” and “Sunshine on My Shoulders” that unabashedly and exuberantly celebrated the magnificence and simple beauty of nature.