The game used randomised ambient sounds and noises, such as evil laughter, chains rattling, distantly ringing bells, and water dripping in addition to the background music to further enhance the atmosphere.

Three brothers (D'Sparil, Korax, and Eidolon), known as the Serpent Riders, have used their powerful magic to possess seven kings of Parthoris, turning them into mindless puppets and corrupting their armies.

While the Sidhe retreat, one elf (revealed to be named Corvus in Heretic II) sets off on a quest of vengeance against the weakest of the three Serpent Riders, D'Sparil.

He travels through the "City of the Damned", the ruined capital of the Sidhe (its real name is revealed to be Silverspring in Heretic II), then past the demonic breeding grounds of Hell's Maw and finally the secret Dome of D'Sparil.

The gameplay of Heretic is heavily derived from Doom, with a level-based structure, an armor system, triggers which open concealed chambers filled with enemies, and an emphasis on finding the proper keys to progress.

Raven added a number of features to Heretic that differentiated it from Doom, notably interactive environments, such as rushing water that pushes the player character along, and inventory items.

As with Doom, Heretic contains various cheat codes that allow the player to be invulnerable, obtain every weapon, be able to instantly kill every monster in a particular level, and several other abilities.

Brian Raffel, the game's director and vice-president of Raven at the time, revealed that the developer first came to id's attention with the release of its debut title Black Crypt.

"[6] Heretic began development in March 1994 with Ben Gokey as lead programmer and a rough storyline penned by Michael Raymond-Judy that was finalized by the game's publisher.

[8] Major additions to the engine for graphics and gameplay included an expendable inventory system; the ability to look up, look down, and fly; water and wind effects on the player character's movement; and improved audio for both ambient and localized sound.

The retail version, Heretic: Shadow of the Serpent Riders, was distributed by GT Interactive in 1996, and featured the original three episodes and two additional episodes:[9] The Ossuary, which takes the player to the shattered remains of a world conquered by the Serpent Riders several centuries ago, and The Stagnant Demesne, where the player enters D'Sparil's birthplace.

On January 11, 1999, the source code of the game engine used in Heretic was published by Raven Software under a license that granted rights to non-commercial use, and was re-released under the GNU GPL-2.0-only on September 4, 2008.

"[18] While remarking that Heretic is a thinly-veiled clone of Doom, and that its being released in Europe after its sequel and with Quake due out shortly makes it somewhat outdated, Maximum nonetheless regarded it as an extremely polished and worthwhile purchase.

They particularly highlighted the two additional episodes of the retail version, saying they offer a satisfying challenge even to first person shooter veterans and are largely what make the game worth buying.