What it is:
The first (and best-selling) LP by UK band Godflesh. It has a distinctive orange/black cover: a simple, low-resolution image of flame and crucifixion. Released in 1989, it has been quite genre-defining, partly due an inclusion on Earache's popular "Grindcrusher" compilation, and partly because it is very, very good. A hot contender for most influential industrial album ever.
What it's like:
Fan accolades constantly use the word 'brutal' and the phrase 'ahead of it's time'. The music is based around very simple, brutal (yes!) loops. The sounds are provided by a drum machine, guitars and harsh, barely intelligible vocals. At times, these are interwoven with found noise, vocal samples etc. to create some fairly densely textured soundscapes.
Precursors:
Napalm Death - obviously. Justin Broadrick was one of the founders of ND when he was about twelve. He decamped quite early on, and showed disdaim for ND's subsequent output.
My Bloody Valentine - less obviously. Some similar elements. I'm not familiar with their earlier work, but the Glider EP (also from 1989), uses many of the same sounds and techniques... with entirely different results.
The Cure - their 1982 LP Pornography is surprisingly similar to Streetcleaner. Both albums feature pounding, bassy drum-machine loops, grinding riffs and unsettling samples. Perhaps more importantly, both albums have some variety in the music, yet maintain the same bleak mood throughout.
Spawned:
The most similar sound I know of is Pitchshifter's 1991 album 'Industrial'. I rather like this album, despite Pitchshifter being basically a Godflesh tribute band at the time. The homage is very clear - the two albums are close to identical in musical and lyrical style, and even in the choice of sampling subject (the ramblings of serial killers).
Snippets from fan reviews (cdnow):
Godflesh take the basic mechanisms of death metal, industrial (think Throbbing Gristle, not NIN), and psychedelia and tear that machinery apart - only to reassemble the collected elements in a completely idiosyncratic fashion. At the time there wasn't another band on Earth who sounded like Godflesh - now there are legions of copycats and followers, and this album has "influenced" so many musicians it is ridiculous.
Listening to the album, musicianship is about the last thing you'll notice. The music is so dark and oppressive that you can't help but be drawn in. Godflesh's sound features feedback-laden guitar riffs, a booming bass and drum machine, and often indecipherable vocals which growl about life, pain, hell, and who knows what else... the album grabs your attention for its entire hour-long duration of gloominess.
Imagine taking Napalm Death and slowing it down to slow to midpace.
I guess the closest comparison for the non-initiated would be a darker, slower version of Ministry mixed with a bit of Fudge Tunnel and a bit of the Swans. | 
