Luther was an amazing vocalist. I'm not a big fan of his solo career either (a bit too slick for me), but I always had the deepest respect for him, because he could write great songs and had an amazing voice.
He played an important part on David Bowies Young Americans album (even co-writing Fascination) and he also wrote Brand New Day (the hitsong from the 'The Wiz' movie with Michael Jackson & Diana Ross).
He had many problems with his health. He's cured now.