As much as I love Glenn (since I was a kid hearing my brother's Deep Purple album) as much I can't stand him "alone"..for me he will always be "the other higher pitched soul voice/counterpart" of David's deep soul voice on these legend three Purple albums..
Male singers like him need "a deeper counterpart".Ofcourse always in my very personal opinion.But I can't stand such high pitched male voices.One reason I could never really dig Rush or Pawlov's dog.