Produced by Gorillaz, Danger Mouse, Jason Cox, and James Dring, it features De La Soul, Neneh Cherry, Martina Topley-Bird, Roots Manuva, MF DOOM, Ike Turner, Bootie Brown of the Pharcyde, Shaun Ryder and Dennis Hopper.

As with the band's eponymous 2001 debut, Demon Days and its performances were accompanied by various multimedia, including interactive features on the Gorillaz website, animated music videos and animatics.

[4] The album spawned the singles "Feel Good Inc.", "Dare", "Dirty Harry", "Kids with Guns", and "El Mañana".

[10] While Jamie Hewlett was working with his team on a script for a possible Gorillaz movie, Damon Albarn was still recording Think Tank with Blur.

And then you wake up in the morning with this nightmare in your head and it's blue sky and beautiful sand, which looks fantastic now but was probably something else millions of years ago.

"[15] As on Gorillaz, there are plenty of guest collaborators, including rappers De La Soul, Bootie Brown from the Pharcyde, and MF Doom along with Ike Turner on keyboards, the singer Shaun Ryder from Happy Mondays and the actor and director Dennis Hopper, who narrates a parable ("Fire Coming Out of the Monkey's Head") about innocence, greed and retribution set to a droll reggae bounce.

[citation needed] Sputnikmusic wrote that the album's style "is a strong foray into the melding of hip hop into pop and rock music.

"[19] Vice called the album a "British pop masterpiece", and wrote that its music "flits between UK rap, alternative rock, piano-pop, trip-hop, reggae, and Beach Boys psychedelia".

[22] Robert Christgau labelled the album "pop trip-hop",[23] while Happy Mag listed it as a key work in the art rock style.

The album also has many lyrical themes centered on the destruction humans are causing worldwide; speaking about the track "Fire Coming Out of the Monkey's Head", Albarn explained, "That came from a very naive idea, which is: what is going to happen when they've taken all of the oil out of the earth?

[27] The limited edition of the album includes a DVD containing the video, audio commentary and an animatic for the music video "Feel Good Inc.", short animated films featuring the band, an exclusive audio track titled "The Swagga" and online access to exclusive sections of the band's website, with various wallpapers and screensavers,[28] as well as a crowbar, facilitating the opening of a locked cupboard in the kitchen on Gorillaz.com in order to download the song, "Happy Landfill".

Fans could submit their photos of ways to spread the message by using graffiti or by sticking "Reject False Icons" stickers that were available for a limited period from the site and from selected record shops in the UK.

Irina Bolshakova aka Schneeflocke created her own artistic interpretation of "El Mañana", featured on an insert included on the DVD version of the single.

[citation needed] At Metacritic, which assigns a normalized rating out of 100 to reviews from mainstream critics, Demon Days received an average score of 82, indicating "universal acclaim".

"[33] Paul Mardles of The Observer felt that, compared to Gorillaz, the songs on Demon Days were more "fully realised and pregnant with ideas", and that the album may prove to be Albarn's "masterwork".

"[34] Los Angeles Times critic Robert Hilburn stated that Albarn's "evocative words, compelling if understated melodic sense and subdued vocals" are at the emotional center of Demon Days, "transcending the gimmick even more than on the first Gorillaz album.

"[36] Rob Mitchum of Pitchfork felt that while Demon Days was uneven, Albarn's experiments "fit together just often enough to again make Gorillaz more than mere Adult Swim novelty.

"[39] In a mixed assessment, Alex Mar of Rolling Stone described Demon Days as "hit-or-miss" and felt that Albarn's "phoned-in and incredibly flat" vocals weighed the record down.

[41] In contrast, Uncut stated that the album featured "great beats, brilliant production, top tunes and some of Albarn's best singing.

"[44] Robert Christgau of The Village Voice gave Demon Days a three-star honourable mention, indicating "an enjoyable effort consumers attuned to its overriding aesthetic or individual vision may well treasure", and selected "All Alone" and "Dare" as highlights.

[23][45] "Feel Good Inc.", the lead single from Demon Days, won the Best Pop Collaboration with Vocals accolade at the 48th Grammy Awards.

[49] Demon Days was voted the 21st best album of the year in The Village Voice's annual Pazz & Jop critics poll for 2005.

[58] Despite its only modestly positive reception at release, Demon Days is now considered to have left an indelible mark on alternative music and has since been variously hailed as "iconic",[59] "classic",[60] "timeless"[61] and a "modern masterpiece".

[62] Multiple writers have noted how Demon Days' commentary was prescient for outlining social and environmental issues in the following years of the 21st century.

In an eleventh-anniversary retrospective, Angus Harrison wrote for Noisey UK that while at the time the record was perceived as "corny, ranty, and hysterical," and even "pretentious twaddle," it is now viewed as "scarily prescient" and "a thrilling allegory set on the precipice of an increasingly dark stretch of modern history.

"[4] In Vinyl Me, Please's Liner Notes series, Kyle Kramer called the "tormented, large-scale questions" of the album "more relevant than ever," whether in "2017 or much further down the line.

"[63] John of audiosnobbery pens that "this doomsday scenario was simply viewed as a self-indulgent and pretentious move from Albarn, but, 14 years later, the messages and problems explored in Demon Days are more pertinent than ever: overpopulation, false gods, guns, violence, depression, corruption and greed.

"[64] Hatim Hafid of River Beats Dance describes that "Demon Days acts as a direct societal critique on colonialism and invasion.

It highlights the negative practices used to exploit countries in the name of democracy and peace", and "...Demon Days remains as one of the most politically charged pieces of the era.

[71] In 2020, the song "Dirty Harry" trended on video-sharing platform TikTok, featured by users conceptualizing themselves as cartoon characters (referencing Gorillaz' virtual nature).