Gameplay is similar to previous Sonic games, featuring fast-paced platforming and ring collecting, but introduces third-person shooter and nonlinear elements.

Sega Studios USA chose to make a game featuring Shadow to capitalize on his popularity and resolve plot mysteries that began with his introduction in Sonic Adventure 2 (2001).

Shadow the Hedgehog was written and directed by Takashi Iizuka and produced by Yuji Naka, with music by Jun Senoue.

Iizuka strove to attract an older audience; Shadow's character allowed the team to use a darker tone and elements otherwise considered inappropriate for the series.

Like previous games in the Sonic series, basic gameplay involves running quickly, collecting rings, tricky platforming and destroying enemies.

[2][4] Although Shadow can outrun the game's vehicles, the latter have unique capabilities, such as crushing enemies and traversing otherwise impassable acid-covered areas.

[2] The game includes a two-player mode[12] that retains the single-player mechanics but is set in one of three specially designed stages and uses a vertically split screen to separate each player's view.

[9] Shadow the Hedgehog, the protagonist, was created fifty years before the game's events by Prof. Gerald Robotnik in an orbital military research space colony known as the ARK.

To his horror, Shadow witnessed GUN raid the ARK and shoot his best friend and granddaughter of Gerald, Maria Robotnik, killing her.

When completing "Dark" missions, Shadow helps either Black Doom or Doctor Eggman, each of whom wants the Chaos Emeralds for himself.

Shadow suffers from amnesia, only able to remember two things: his name and his attempt to escape the Space Colony ARK with his creator Gerald Robotnik's granddaughter Maria, who was killed by GUN soldiers.

[11] The missions completed determine which one of ten possible endings will be seen after Shadow collects all the Chaos Emeralds and defeats one of the game's final bosses.

[29] Shadow kills Devil Doom[30] and uses Chaos Control to teleport the Black Comet back into Earth's orbit, where he obliterates it using the Eclipse Cannon.

[13] The team felt that Shadow's design—inspired by films such as Underworld, Constantine, and the Terminator series—would make the story darker and allow for elements, such as vehicles and weapons, otherwise considered inappropriate for a Sonic game.

[42] The music of Shadow the Hedgehog was composed by Jun Senoue, with additional work by Yutaka Minobe, Tomoya Ohtani, and Mariko Nanba.

Lost and Found: Shadow the Hedgehog Vocal Trax is a video game soundtrack album released on CD on February 22, 2006.

In addition to this, an alternate music video for "Tripod Baby" featuring the remix included new scenes with Shadow.

[47][48] Unlike most Sonic games, Shadow the Hedgehog's dialogue features mild profanity, including damn and hell.

[58] Game Informer staff writer Matt Helgeson said, "not only is this new 'adult' interpretation of Sonic painfully dumb, it's also ill-advised and almost feels like a betrayal to longtime fans.

"[54] Eurogamer staff writer Tom Bramwell felt that "the game's other selling point – its darker edge – [is] not really meant for us.

[55][60] In contrast, Nintendo Power staff writer Steve Thomason rated the game 8.0 out of 10, stating, "this darker take on the Sonic universe succeeds for the most part, giving the series a bit of an edge without going overboard on violence.

"[59] Helgeson panned the game's "laughable" plot, saying it "makes no sense," and that various Sonic conventions undermined its attempts to be "mature" or "edgy".

Greg Mueller of GameSpot felt that the guns were nearly useless because of a lack of a target lock or manual aim, combined with an ineffective auto-aim.

[52] Casamassina disliked the "stupid level design", saying that "[j]ust because they dazzled players six years ago does not mean that Sonic Team can copy and paste exactly the same loops and spins into each new franchise iteration and expect everyone to be happy with the outcome.

"[56] GameSpy observed that "the areas are much less open than in previous Sonic games, but the level designers haven't taken advantage of the constraints.

[15][58][59] GameSpot praised the variety of alternate endings, but concluded that "the gameplay isn't fun enough to warrant playing the game through multiple times.

Shepard praised the game's multiple branching narrative paths as "really compelling", calling its mission structure a "natural evolution" of the alternate story campaigns featured in other Sonic games of the time and saying it allowed players to "explore the deep (if overly convoluted) backstory of the antihero".

However, Shepard also admitted that "some of [the] hate is deserved", criticizing the gunplay as "frustrating" and the vehicles as pointless, as it was generally faster to simply run as Shadow on foot.