Oblivion and Skyrim were certainly great -but pretty derivative.
Morrowind was Jeremy Soul's major breakthrough into legendary status. Even today whenever I want to get an unwanted song out of my head I just play the Morrowind theme in my mind and it takes over completely.
Even before that he was seriously carrying great games to a whole new level though. Particularily in Total Annihilation and Icewind Dale which established him as the biggest name in gaming as far as music went.
Walking into Kuldahar for the first time set the whole tone of the game so otherworldly and mystical, it hypnotised everyone right from the start and set the stage for an amazing game, and the soundtrack just never really let up from there.
Total Annihilation was definitely what launched his career though. An orchestra hadn't really been used much for a gaming soundtrack prior to this, at least not that I'm aware of. And was the main reason for Total Annihilation needing two disks. The standard at the time was mostly digital music with some occasional instrumentation thrown in. Jeremy's soundtrack was all so chaotic and bombastic, it fit perfectly with all the explosions and shrapnel as one army of ~160 units crashed into another with sirens going off and the screen shacking wildly in response to the utter chaos, set to Jeremy's absolutely perfect score. There were whole articles in magazines dedicated
soule-ly to praising his work in the game.
By the time Morrowind was coming out, Jeremy's name being attached to the game was already enough to carry much of the hype, and the result really just cemented him as one of the best video-game composers of all time.
Kevin Manthei, composer of the soundtrack for Civilization 2 was pretty great too.
He was really good at creating unique sounds to fit whatever project he was given. Some of his other works of note, being Twisted Metal black, Vampire: The Masquerade, and my personal favourite game of all time and name-sake, Shiny's Sacrifice. All great examples of his diversity (though often dark and brooding), they really enhanced the themes and atmosphere the games were going for perfectly.
and also the music of the second monkey island...
They also gave it a nice update in sound quality with the SE versions in the last years.
Peter McConnell! Brilliant work all over the place, my personal favourite definitely Grim Fandango, and Psychonauts. He hasn't gone wrong in any game really though.