The double-disc album featured a large selection of guest appearances, including Bone Thugs-n-Harmony, Mariah Carey, the Marley Brothers, Big Pun, Fat Joe, Cuban Link, Gangsta Boo, E-40, 8Ball & MJG, Kurupt, Treach and Snoop Dogg.

Stephen Thomas Erlewine from AllMusic wrote: "Krayzie doesn't hesitate to accentuate the already smooth surfaces of his music.

The journalist criticized the excessive length of the album, calling it "ridiculously inflated" and adding that "there are enough songs to make a very good record, possibly one of the best things Krayzie has been involved with".

He highlighted fast rapping on the track "Heated Heavy", saying that "Krayzie could give Twista a run for his money any day.

"[7] Soren Baker, in his review for Los Angeles Times, wrote that "the husky-voiced rapper keeps pushing the music's aural boundaries", commending both the production that features "an eclectic range of instruments" and Krayzie Bone's vocal delivery.

[6] Kris Ex of Rolling Stone described Thug Mentality 1999 as "self-indulgent – but consistently engaging", while also taking issue with some of its lyrical content, such as a "vivid date rape" in the track "Look At You Now", which he named "one of the most disturbing moments ever put to wax".

[8] Charlie R. Braxton of The Source believed that with this album Krayzie Bone takes a "gigantic step toward establishing himself as a soloist of the highest caliber", praising his vocal performance, ranging from "hard-core and rapid-fire to the softer, more sing-songy".

[9] This was also highlighted by USA Today's Steve Jones, who believed that the artist "shows himself adept at a variety of delivery styles".