Shlomo, the singing rabbi (HaRebbe Hashir) was the charismatic rabbi who used his songs to attract (mekarev) Jews into the orthodoxy. He was a VERY controversial figure.
Considered the father of modern Jewish music, he inspired other figures, like Rebbetzin Ester Jungreis, to become active in
attracting Jews back into the orthodoxy. Shlomo is said to have attracted thousands of people all by his lonesome.
Originally, Shlomo was learning at some of the premier Torah institutions in America, including Lakewood Beth Medrash Gevoha
(lead by Aron Kotler) and Torah Vodaath (he got his smicha there from Rav Kutner). But he left Lakewood to go to Lubavitch because they were already doing outreach and Shlomo wanted to learn how to do it from them.
Shlomo couldn't abide by the Lubavitchers strict rules about
Kol Isah, etc. and left Lubavitch to strike out on his own.
Shlomo was known for hugging and kissing people during his concerts, including women and for that incurred the wrath of the orthodox community. He also alienated his former allies because of his "hippy rabbi" stance.
More recently, there was an article in Lillith magazine (see Rick's site under Chabad Lubavitch and Ultra-Orthodox groups)
about the Rabbi's indiscretions with women.
Although he was a charitable person and reputedly died penniless having given away all his wealth to charity, there were severe character flaws in his nature.
Also, a lot of his stories revolving around various miracles are subject to extreme question. In fact, most of those stories never made it to his recordings until the very end of his life and after.
Almost eight years after his death, new releases of his music are still coming out and many new communities using his music for their nusach are spreading.
I lived at his Moshav Modi'in during the late '70s and know quite a few of his chasidim. Being associated with him caused me problems at Yeshivat D'var Yerushalayim (see my document about that institution).

I used to go to many Shlomo concerts when he was in the NYC and LI areas. I was about 15 when I met him. I was usually headed off by some orthodox Rabbi, who definitely didn't want me around him.
I'm damned if I do, and damned if I don't try to be orthodox.
After what I went through in public school, I wanted to know that some orthodox leader actually gave a hoot about me.
Some of my relatives kept telling me to leave Shlomo alone.
This despite the fact that he made himself very accesible to the common folk. "[He] is a big, important man and he's very busy", etc.
I think what happened to me in relation to Judaism is important to relay to others. It seems to me that no one should put himself out on a limb to get persecuted like I did. Especially if you don't get much benefit out of orthodoxy.

Quite a few years ago, I was at Penn Station in NY waiting for a train back to LI, NY. I had my guitar and the Shlomo song book
(the first one now out of print). Someone noticed it and came up to me telling me that he was involved with the BT movement but left it because of Shlomo.
Shlomo had boundless energy and he burnt that guy out as he related to me. I felt that too.