Although Glen was primarily popular due to his several "hit" songs, he was also a fantastic guitarist and songwriter. He played on recordings by the Beach Boys, Bobby Darin, Ricky Nelson, Dean Martin, Nat King Cole, the Monkees, Nancy Sinatra, Merle Haggard, Jan and Dean, Frank Sinatra, Ronnie Dove, Phil Spector and Elvis Presley, just to name a few. He released over 70 albums in a career that spanned five decades, accumulating over 45 million record sales worldwide, including 12 gold albums, four platinum albums, and one double-platinum album. Jimmy Webb, who wrote many of Campbell's hits and worked with him throughout his life, said that Campbell could play with "any guitar player in the world, from George Benson to Eric Clapton," adding that Paul McCartney considered him among the best guitar players. "People will realize what an extraordinary genius Glen really was".