ENTOMBED: LEFT HAND PATH
I could be mistaken on this, but I think this was the first full-length album by a Swedish death metal band using the Sunlight Studio. It has the very familiar buzzsaw guitar sound on the riffs. This was just a small sign of things to come from the Swedish death metal scene as Dismember, Grave, and others began releasing albums and the guitar tone became commonplace. It's influential because it's a great album, not just the tone. Unfortunately Entombed would never put out another album quite as good.
JUDAS PRIEST: PAINKILLER
After a bit of a period of mediocrity, Judas Priest returned in full force on this album. The songs were more engineered to sound like their 1970's output, while adding in elements of speed metal. What resulted was a frenetic and fantastic album of speed and power. Halford never sounded quite as good as he does on this album. Unfortunately, he would leave the band soon after and it would be years before he rejoined them. This is Priest's best album in my mind.
KREATOR: COMA OF SOULS
This is not a particularly special or unique release by Kreator, it's actually just them being Kreator. But the album is great anyway and was the band's last great album before over-experimenting with other styles. This album features the incredible "People of the Lie", which is one of my personal favorite German thrash metal songs. Mille's voice sounds amazing on this album. As I said, it would be years before they got back to this point.
PANTERA: COWBOYS FROM HELL
Here we see the beginning of a powerful career in metal. Pantera had released a few albums before this, but this was the first of their groove metal stage, the most well-known part of the band's history. They had not fully resorted to mid-paced half-thrash at this point. This album still bears marks of power/thrash metal. It is my favorite Pantera album for this reason, and also because "Cemetery Gates" is an all-time favorite song. I was never quite as impressed with the rest of the band's output, maybe it's because this was the first album I heard, maybe it's because this is just simply better, in every way.
SADUS: SWALLOWED IN BLACK
I mentioned in a previous post that thrash was finding new ways of brutality in the late 1980's/early 1990's. This is one of the lead bands from this brutal style of thrash. Sadus plays inhumanly fast. This is the second album from the band, which features Steve DiGiorgio of such great bands as Death, Testament, Autopsy, and Iced Earth. Sadus is so brutal that they oftentimes veer in the direction of death metal.
Honorable mentions: Alice in Chains: Facelift, Anthrax: Persistence of Time, Blind Guardian: Tales from the Twilight World, Cannibal Corpse: Eaten Back to Life, Danzig: II-Lucifuge, Death: Spiritual Healing, Death Angel: Act III, Deicide: Deicide, Forbidden: Twisted Into Form, Iced Earth: Iced Earth, Megadeth: Rust in Peace, Obituary: Cause of Death, Paradise Lost: Lost Paradise, Queensryche: Empire, Slayer: Seasons in the Abyss, Testament: Souls of Black.
Bands that formed in 1990: At the Gates, Cathedral, Dark Tranquillity, Fear Factory, In Flames, Krisiun, Kyuss, Lamb of God, Lost Horizon, My Dying Bride, Opeth, Satyricon, Type O Negative.