"Kill 'Em All" received critical acclaim. Bernard Doe of "Metal Forces" described "Kill 'Em All" as one of the fastest and heaviest albums ever recorded, and remarked that the album is not for the faint-hearted. Greg Kot of the "Chicago Tribune" acknowledged it as the "speed metal prototype", but felt the lyrical replication of Judas Priest and the Misfits kept the album short from becoming a classic. In a retrospective review, "Billboard" praised "Kill 'Em All" for changing the face of popular music with its unique combination of punk and metal. AllMusic's Steve Huey called it "the true birth of thrash". He praised Hetfield's highly technical rhythm guitar style and said that the band was "playing with tightly controlled fury even at the most ridiculously fast tempos". Rob Kemp, writing in "The Rolling Stone Album Guide", credited the album for consolidating the punk rock and heavy metal scenes, but felt that apart from "Seek & Destroy" and "(Anesthesia)—Pulling Teeth", most of the album had the band "trying to look tough" over-enthusiastic but unfinished riff-based songs. Journalist Martin Popoff said "Kill 'Em All" differentiated from the debuts by Metallica's Bay Area contemporaries because the fans could identify with Hetfield's lyrics and the band's appearance. "Spin"s Chuck Eddy considered "Kill 'Em All" the inception of the "extreme metal mania" of the early 1980s. He noted the album did not receive much critical praise at the time of its release but said it aged well and opened the doors for the less commercially successful bands. Although McIver credits Venom's "Welcome to Hell" (1981) as the first thrash metal album, he acknowledged "Kill 'Em All" as a major influence on the flourishing American heavy metal scene. Despite its "less-than-perfect" production, "Loudwire"s Jon Wiederhorn said that "Kill 'Em All" sounds like an "influential slice of history" and stands on the same level as classic albums by Black Sabbath, Iron Maiden, and Judas Priest.