The setting combines alternate history and cosmic horror, with real-world figures making appearances, and each title has multiple endings.

The series saw limited media expansions, with Koudelka in particular receiving both a novelization and a manga continuation based on the initial story plan.

While Koudelka saw mixed reactions from critics, the Shadow Hearts trilogy saw both contemporary and retrospective praise and is Sacnoth's best-known product.

The gameplay of the Shadow Hearts series follows a similar formula; they are role-playing video games featuring the exploration of multiple locations across the world, and turn-based battle systems triggered through both random and scripted encounters.

[21][22] The basic system was established in the first Shadow Hearts, with the next two entries adding new battle elements such as combination attacks and versions of actions that allowed a character to act twice in one turn.

[6][27] Koudelka combines two distinct styles of gameplay; exploration from fixed camera perspectives and puzzle solving similar to earlier entries in the Resident Evil series; and turn-based combat playing out on a grid triggered through a random encounter system.

[33] The original world design drew from several sources, including the writing of Lovecraft, Umberto Eco, William Hope Hodgson and Lord Dunsany.

[6][19] The plots of Shadow Hearts and Covenant are linked by the romance between Yuri Hyuga, a "Harmonixer" capable of capturing and shapeshifting into monsters; and Alice Elliot, an exorcist who holds a key power.

[32][41] His aim was to create an unconventional horror RPG, though he ended up clashing with the game design staff, and following the release of Koudelka resigned from Sacnoth.

[44][45] Machida wanted to create an RPG with Shadow Hearts that fell outside the typical settings of other RPGs, using the world of Koudelka as a starting point and building upon it with original lore.

[46] In response to feedback from the first game, Machida shifted the tone of Covenant to incorporate more humor, making its central theme the pursuit of happiness.

[19][47][48] The focus was on refining and building upon the gameplay mechanics of Covenant rather than changing anything, with the new setting and characters intended to give series newcomers an easy gateway.

[53] While Universal Interactive maintains the Shadow Hearts trademark, the company stated in 2021 that there were no plans to continue the series or remake any of its entries.

[70] The translation of all three Shadow Hearts titles was handled by Jeremy Blaustein, who had previously worked on the Pokémon anime series, Valkyrie Profile and Metal Gear Solid.

[71][72] The music for the Shadow Hearts series was primarily composed by Yoshitaka Hirota, who had earlier worked as a sound designer on Koudelka.

[69][90] Chris Breault of Kill Screen, in an article celebrating the first two Shadow Hearts titles, noted its blend of many conventional elements while being "loyal in the end only to the principle of staying weird".

[14] Anime News Network's Todd Ciolek noted that Shadow Hearts was Sacnoth's best-recognised product and stood out during the PS2 era against other RPGs.

[93] Contemporary reception of Koudelka was mixed, with many praising its storyline and characters while faulting its gameplay and graphics compared to other titles of the time.

[28][29][30] Shadow Hearts was praised for its narrative and the Judgement Ring mechanic, but many faulted its graphics at inferior to other titles for the time and disliked other elements of its gameplay.

[5] A novelization, Koudelka - The Mansion's Scream by Nahoko Korekata, was published by ASCII Media Works in February 2000 as part of its Famitsu Bunko imprint.

[115] In 2022, Machida, Kato, and Hirota later co-launched a Kickstarter campaign for a spiritual successor titled Penny Blood, featuring similar mechanics to the Shadow Hearts series.