Answer by taking a quote from the following article:

MC5 was an American rock band from Lincoln Park, Michigan, formed in 1964. The original band line-up consisted of vocalist Rob Tyner, guitarists Wayne Kramer and Fred "Sonic" Smith, bassist Michael Davis, and drummer Dennis Thompson. "Crystallizing the counterculture movement at its most volatile and threatening", according to AllMusic critic Stephen Thomas Erlewine, the MC5's leftist political ties and anti-establishment lyrics and music positioned them as emerging innovators of the punk movement in the United States.

Playing almost nightly any place they could in and around Detroit, MC5 quickly earned a reputation for their high-energy live performances and had a sizeable local following, regularly drawing sellout audiences of 1000 or more. Contemporary rock writer Robert Bixby stated that the sound of MC5 was like "a catastrophic force of nature the band was barely able to control", while Don McLeese notes that fans compared the aftermath of an MC5 performance to the delirious exhaustion experienced after "a street rumble or an orgy". (McLeese, 57)  Having released a cover of Them's "I Can Only Give You Everything" backed with original composition "One of the Guys" on the tiny AMG label over a year earlier, in early 1968 their second single was released by Trans-Love Energies on A-Square records (though without the knowledge of that label's owner Jeep Holland). Housed in a striking picture sleeve, it comprised two original songs: "Borderline" and "Looking at You". The first pressing sold out in a few weeks, and by year's end it had gone through more pressings totaling several thousand copies. A third single that coupled "I Can Only Give You Everything" with the original "I Just Don't Know" appeared at about the same time on the AMG label, as well.  That summer MC5 toured the U.S. east coast, which generated an enormous response, with the group often overshadowing the more famous acts they opened up for: McLeese writes that when opening for Big Brother and the Holding Company audiences regularly demanded multiple encores of MC5, and at a memorable series of concerts, Cream -- one of the leading hard rock groups of the era -- "left the stage vanquished". (McLeese, 65) This same east coast tour led to the rapturous aforementioned Rolling Stone cover story that praised MC5 with nearly evangelistic zeal, and also to an association with the radical group Up Against the Wall Motherfuckers.  MC5 became the leading band in a burgeoning hard rock scene, serving as mentors to fellow South-Eastern Michigan bands The Stooges and The Up, and major record labels expressed an interest in the group. As related in the notes for reissued editions of the Stooges' debut album, Danny Fields of Elektra Records came to Detroit to see MC5. At Kramer's recommendation, he went to see The Stooges. Fields was so impressed that he ended up offering contracts to both bands in September 1968. They were the first hard rock groups signed to the fledgling Elektra.

What did people think of them?
sellout audiences of 1000 or more.