The entire first episode, "City of the Damned", makes a strong impression with all of its music, but here are some stand-out tracks for the sake of highlights:
E1M1: The Docks has an eerie yet dance-worthy beat. It was so memorable it got a catchy remix in Hexen 2 for the Temple of Horus level.
E1M2: The Dungeons could be described as festive yet creepy, switching from an upbeat to a sinister tune. Fitting for the action-packed battles through the titular dungeons.
E1M5: The Citadel is appropriately frenetic for a level where you're surrounded by hostiles and need to rush for cover to avoid a quick death.
E1M7: The Crypts sets the mood for approaching the end of the episode with a grandiose cinematic track.
E1M9: The Graveyard (secret level) is very fitting for the cemetery that it takes place in; gloomy yet energetic. It's also played on D'Sparil's stage, so you'll get to hear it if you missed the secret level the first time, and it works well as a Final Boss score.
"Hell's Maw", the second episode, has mostly unique tracks:
E2M2: The Lava Pits is notable for working well with the restrictive limitations of the OPL synthesizer to generate a cinematic experience to accompany the lava cavern theme of the level.
E2M3: The River of Fire is upbeat and very fitting for your trips around the titular stream of lava.
E2M7: The Great Hall conveys a sense that you're nearing end of the episode, and gets you energized for the climax.
E2M8: The Portals of Chaos signifies the approaching final fight of the episode and adds a sense of tension to the battle against the Maulotaurs.
Track 2 of Heretic 2 has a haunting quality to it. It's both sad and menacing at the same time, serving as the perfect pulse-pounding boss music.
has an eerie yet dance-worthy beat. It was so memorable it got a catchy remix in Hexen 2 for the Temple of Horus