He was well known for his niggunim and being on the hippie scene during the Baal Teshuva Movement. Many minyanim around the world either occasionally or more often have services in a carlebachian style.
I don’t think this question would lead to anything constructive. We are bidden not to denigrate those who are no more among the living (unless… which is not nogea here). This is a very touchy subject, and is bound to turn both directions…
For myself, I don’t listen to recordings of Carlebach. I don’t like his voice. But some of his music has grown on me, and I do sing his songs at times. When davening for the amud, his songs are good to use, as they are generally well known, so people will sing along.
“Bal Teshuvah Movement” always irks me. I understand people like labels. But somehow it is the N word of Judaism. I just really dislike labels especially ones that people use to make themselves feel superior.
LF: I have heard big Rabbonim say that “ashon Hara isn’t Shayach in cases like this because one could C”V come to learn from the bad things that well-respected people whose bad things weren’t known.
Rav Moshe wrote a teshuva supposedly about Carlebach, although he does not mention his name. It’s “understood” who Rav Moshe was talking about. Teshuvot Iggerot Moshe, Even Ha-Ezer, I, no. 96
I don’t have it in front of me, nor can I find it on Hebrewbook.org.