Released in 1999, it represented a large step towards a more electronic sound for the band and received a huge critical acclaim.

[12] Recording was finished at a small studio near Littlehampton, putting the final touches on vocals.

In the words of guitarist Stu G, "Martin and I went out to LA in January for three weeks and sat down with him and explained to him what we were doing and where we were coming from, what we were trying to accomplish with the music.

"[9] Puig's mixing of the album deepened the bass sound and brought it more of a "club" feel.

[12] As with the previous album, King of Fools, Mezzamorphis is mostly midtempo; notable exceptions include "Bliss"[16] and "Gravity".

[17] The new electronic direction taken by the band incorporated a theremin, played by bassist Jon Thatcher; additionally, Stu G used Revox tape delays to create keyboard-like guitar effects.

While Mezzamorphis is not strictly a concept album, more than one professional reviewer has pointed out that there is a general theme of getting to heaven running through the whole work.

"[16] The first track, "Mezzanine Floor", is the change-oriented centrepiece of the album, written about the musical growth of the band.

[12][13] Another strong theme from the album is peer pressure, particularly due to the band's part-Christian-part-mainstream status.

"Bliss" deals with accusations of selling out; in the words of Stu G, "we know exactly where we want to go, we want to take our music to the world and have it recognized as being as good as anything that's out there.

Rock Sound magazine praised "the band's talent for writing instant rock/pop songs"[29] and stated, "it shouldn't be long before Delirious?

claim their rightful place as one of Britain's brightest new bands",[30] whilst Q magazine named them "the hottest thing in Christian rock"[31] and predicted, "Mezzamorphis will be the album that makes them".

[32] The UK Christian music magazine Cross Rhythms awarded the album a full ten-square rating, calling the album an "absolute classic",[17] whilst Jesus Freak Hideout stated, "the musical growth is evident... and appreciated".

[13] Additionally, the album caused some controversy in the US Christian music scene[12] due to the lyric "she's as pretty as hell" in the song "It's OK".

[13][38] "We recognise the ultimate validity of the criticisms leveled against us," responded lead singer Martin Smith, "and we feel as a band that this just speaks to the spiritual and intellectual maturity of our listening audience and Christians in general, for that matter.