Sonic Frontiers

Sonic Frontiers is a 3D platformer and action-adventure game. As Sonic, the player explores the Starfall Islands (which consist of various biomes, including flowery fields, forests, ancient ruins and deserts) to collect the Chaos Emeralds and investigate the islands' relationship to them. Sonic retains his abilities from previous Sonic the Hedgehog games: he runs at high speeds, collects rings, grinds on rails, and homes in on enemies to attack. The player can double jump, sidestep, drop dash, and boost if Sonic has enough energy.

New abilities include combat attacks, running alongside walls, and using the Cyloop to create a circle of light around objects and interact with them. The Cyloop can perform different tasks by drawing certain shapes — for example, drawing an infinity symbol or a number 8 will allow Sonic to boost indefinitely for a short time. Sonic also gains the ability to temporarily boost indefinitely upon collecting the maximum number of rings. The player can customize the controls and adjust the game's difficulty along with Sonic's speed, turning, acceleration, and sensitivity, among other things.

Doctor Eggman travels to the abandoned Starfall Islands archipelago to steal technological secrets created by the Ancients, ancestors of the Chao. When he uploads his artificial intelligence unit, Sage, into a portal, several robotic defense units are summoned. Detecting a threat signature, Sage ceases hijacking the portal and initiates a protection protocol, drawing the Chaos Emeralds to the islands and dragging Eggman into an artificial dimension called Cyber Space.

Sonic, Tails and Amy investigate the Chaos Emeralds' recent activity, but their plane is sucked into a wormhole to Cyber Space. Sonic escapes to the islands in the real world, where a disembodied voice tasks him with finding the emeralds and destroying the island's robotic Titans to remove the boundary between the real and digital worlds. Believing this will save his friends – including Knuckles, who was transported there while exploring the ruins above Angel Island – Sonic releases their digital forms from cages created by Sage, who works to free Eggman from Cyber Space; destroying the cages causes Sonic's body to become increasingly corrupted. Sage cautions Sonic to leave, influencing the islands' mechanical guardians and Titans to attack him, but grows to sympathize with him while observing his interactions with his friends. Meanwhile, she and Eggman form a mutual familial bond.

Following the release of Sonic Forces (2017), Sonic Team began exploring approaches for its next Sonic the Hedgehog game. In addition to celebrating the series' upcoming 30th anniversary, the developers sought to define what a modern Sonic game should be and solidify the series' direction for the next decade. Iizuka felt the series needed to take an innovative direction that would lay the foundation for future games, similar to how Sonic the Hedgehog (1991) and Sonic Adventure (1998) set templates used by later games. Forces received criticism for its short length and level design, so its director, Morio Kishimoto, concluded that the team's method of designing levels originating from Sonic Unleashed (2008) would no longer satisfy fans.

Sonic Team ultimately determined that the series' traditional linear design contained "little room for evolution" and felt it could not progress in this direction. In particular, Takashi Iizuka, the head of the development team and the producer of the Sonic series, felt 3D Sonic games were not giving players enough freedom and constrained them to linear paths. He stated that the goal with Frontiers was to "evolve the linear, stage-clearing 3D action [...] into a new action-packed adventure game where players have the freedom to explore the environment around them".

Nintendo Life characterized early Frontiers gameplay footage as divisive. Kotaku felt the game looked fine but derivative and bland, lacking the series' unique identity, and Polygon and Nintendo Life found the open world desolate. Some fans demanded the game be delayed, and the hashtag #DelaySonicFrontiers briefly trended on Twitter. Iizuka said that Sonic Team expected early reactions to be polarized, as he felt the early footage would not give fans a good idea of what to expect.

According to the review aggregate website Metacritic, the PlayStation 4 version and Windows version of Sonic Frontiers received "generally favorable reviews", while other console versions received "mixed or average reviews".