A quick breakdown:
Snake - Vocals
Piggy - Guitars
Blacky - "Blower Bass"
Away - Drums (plus all lyrics, stories and artwork)
War and Pain (1984):
Slightly experimental, but basically a screamo punk/thrash album
RRROOOAAARRR!!! (1985)
Less experimental. Purely a screaming thrash punk album. The lyrics are the only thing proggish about these first two releases. All of the first four albums tell the continuing story and adventures of the Voivod character.
Killing Technology (1987)
Still maintaining the thrash style vocals...but the music changes significantly. Longer, more experimental tracks...deeper arrangements...and the infusion of jazz stylings. Still pretty thrashy...but this is where Voivod *really* begins for me.
Dimension Hatross (1988)
My favorite album. First album with clean vocals. Most rhythm and timing experiments yet. Final album in the story of the Voivod.
Nothingface (1989)
Most people consider this album to be their masterpiece. Still metal...but what little thrash remained on Dimension Hatross is completely gone here. There's a *brilliant* cover version of Pink Floyd's "Astronomy Domine"...and that pretty much captures the mood of this entire album. A brilliant blend of Pink Floyd and metal.
Angel Rat (1991)
Produced by Terry Brown. Possibly *a bit* mellower than Nothingface...but mostly very similar. Great album...fantastic album. But misses Nothingface's brilliance by a hair.
The Outer Limits (1993)
To be honest, I havn't heard it. I've heard great reviews. Most people say it's their proggiest album of all....and with the 17 minute song "Jack Luminous" it's hard to argue. At the time the album came out, I was just caught up in other things. This is the first album without the original bassist "Blacky" (the first sign that there was trouble within the band) It was recorded as a trio. The band was a mess, but the album is a cult classic. They briefly broke up after this album.
Negatron and Phobos (1995 and 1997)
Piggy and Away decided to replace Snake and Blacky with a single bass player/lead singer Eric Forrest. Recorded as a trio. Eric's vocals are a return to the screamo/cookie monster vocals of the first three albums. I never got into it. I'm not against screaming vocals...it just wasn't Voivod any more to me. The band broke up again.
Voivod, Katorz and Infini (2003-2009)
Jason Newsted joined Voivod as "Jasonic" on bass and original vocalist Snake came back. I've heard very little of these albums. Some songs are better than others. The stuff from the first self titled album sounded pretty awesome. But Piggy died in 2005. Katorz was recorded while he was still alive, but released posthumously. Infini was pieced together from Piggy's final demos. Most people thought they were done.
The tour with Daniel (Chewy)...and Blacky coming back after 20 years motivated them to write new stuff. I think having all the living original band back together again with an old friend from their clubbing days bodes well for new material. But only "The Unknown Knows"...
I would also add that if anyone is a fan of early thrash. (i.e. If you love albums like Kill Em All, Fistful of Metal, Show No Mercy, early Motorhead, Venom, Sodom, Destruction material...) Then you really need to hear War and Pain. You wouldn't even recognize it as the same band who recorded Nothingface...but it's a pretty cool album in its own right.
One of the cool things about this band is how drastically they changed over the years. Their first two albums sound like awesome Venom demos (awesome if you like Venom) and then in the course of just five years and five albums, they completely shift to one of the most experimental trippy Floyd-metal bands of the late 80's. Yet each album seems like a natural predecessor to the next. It was cool hearing them from the beginning and growing with them.