Dummy became a negative influence precisely because it was so good - just like Nirvana gave birth to horrendous bands like Pearl Jam, it was responsible for everything from Sneaker Pimps' pop-hop to Robbie Williams doing Bond-theme-esque stuff. But if you forget the coffee bar ubiquity and rash of 90's "female folk-soul singer does guest appearance on indietronica LP", you'll hear a truly epochal record.
Portishead are post-modern with a difference, in that they hearken back to pop and rock's romantic era (60's/70's) yet use sampling and po-mo techniques in their own striving for novelty and authenticity, recreating the nostalgic sounds of yesteryear but re-contextualising them in a unique hip hop sound-world. In this way they can be seen as an example of Deleuze and Guattari's concept of artistic becoming, where the styles of the past are recreated but become different, are set free from their original context to reveal different forces, at the same time as their own sound is transformed by this curious fidelity to the sounds of the past.
Geoff Barrow freely admits in (rare) interviews that he hasn't seen the films he's sampled, has never listened to the jazz or avant-classical he's supposed to be influenced by, is cripplingly media-shy and sincere (he actually apologised to one interviewer for owning the house he bought on the album sales), and obviously had no idea that his creation would become (briefly) massively trendy. He is as obsessive as Kevin Shields, recording his own sounds live with dogged fidelity to recording techniques of the 60's/70's, then digitally processing them, pressing them to vinyl and re-recording them from turntables weighted down for extra crackle, hum, weight, gravity and pressure, allying these slo-mo soporific atmospherics with an irrational love of hip hop and cinematic sound.
Beth Gibbon similarly rarely did press interviews, caring so little for acclaim that she drunkenly swapped her Mercury statue for a fag after the awards. But she is a virtuoso of vocal style, refusing an authentic "personal" voice in favour of inhabiting different styles, often within a single song. Glory Box for example begins with that famous Eartha Kitt vampire routine then switching abruptly into open-throated soul diva for the chorus. It's this stylistic overload that allows her and us to revel in either the over-blown emotions of tracks like this, or the grain and sound of the voice, without the pressure of believing in an emoting ego behind it. And then from nowhere they detonate their most commercial single with that depth-charge breakbeat-from-hell in place of a middle 8, with Gibbon's distorted wailing tape-echoed over it - one of the more thrilling moments of pop terrorism in recent memory, up there with 'ardcore's anschluss on the charts a few years previously.
The second studio album was the same only more so, the darkness darker, the distortion rougher, the voice more cracked and ravaged, culminating in Half-Day Closing which combines Black Sabbath/King Crimson-esque dynamics with Beth shrieking of the evils of capitalism (I think - "Underneath the fading sun/the silent scheme of a businessman/has left us choking/Dreams/can't believe they've gone") through a distorted Hammond organ Leslie speaker, as if underwater or from another planet.
Kanye West isn't the only hip hop artist to cite them as an influence - one of those Wu-Tang offshoots (Bobby Digital I think) sampled them, and Timbaland has cited their sound/production as an influence (he possibly sampled them somewhere also?). After a Shields-esque lull since there last album who knows what they will sound like next, or what the world will make of it, but in a music-scape devoid of singular acts following a vision I reckon we need them more than ever (Ladytron and maybe Stereo Total are the only other "bands" that I can get excited about; in the post-rave discontinuum it's more about scenes/genres).