Like its predecessor, the game features a large open world and adopts many elements from the role-playing genre, putting more emphasis on combat and exploration than stealth.

Odyssey also continues the story arc of Layla Hassan, a major character introduced in Origins, who relives the mercenary's memories through the Animus device to find a powerful artifact.

Following in the footsteps of Origins, Odyssey facilitated the transition of Assassin's Creed into a series of action role-playing games by introducing player-choice mechanics.

Throughout the game's development, the team was inspired by other contemporary RPG titles including The Witcher 3: Wild Hunt, The Elder Scrolls V: Skyrim, and Fallout 4.

It received generally positive reviews from critics, with praise for its gameplay, graphics, characters, role-playing elements, and world design, but was criticised for its overambitiousness, pacing, and the inclusion of microtransactions.

Odyssey was followed in November 2020 by Assassin's Creed Valhalla, which features a historical setting in medieval England and Norway during the Viking expansion across Europe and which concludes Layla's story arc.

[10][11] While the main campaign missions follow the mercenary as they reunite their family and stop the Cult of Kosmos, additional questlines task the players to defeat mystical creatures from Atlantis and take down cultists.

[35] As with previous games in the series, Odyssey features a narrative set in the modern-day, which follows Layla Hassan, an Assassin and former Abstergo researcher who was introduced in Origins.

[36] Assisted by fellow Assassins Victoria Bibeau, Kiyoshi Takakura, and Alannah Ryan, Layla's goal is to find the Staff of Hermes Trismegistus and the lost city of Atlantis by using data processed by her portable Animus device.

The game's main storyline follows the player character, the elder of two siblings known as the Eagle Bearer, a legendary mercenary with Ikaros as a constant companion.

[37] In conjunction with the Eagle Bearer's attempts to reunite their fractured family, parallel quest lines deal with the destruction of the Cult of Kosmos (a secret organization spanning the Greek world) and the discovery of artifacts and monsters from Atlantean times.

[41] The game features several creatures from Greek mythology, such as Medusa, the Cyclops, the Sphinx, and the Minotaur, depicted here as experiments of the Isu, the same race that created humanity and most of the artifacts encountered throughout the series.

In 2018, Layla Hassan recovers Leonidas' spear and extracts from it the DNA of his grandchildren, Alexios and Kassandra, to be used for her Animus to find the location of the Staff of Hermes Trismegistus.

Myrinne persuades her eldest child to convince the Spartan regime to reinstate their citizenship and ancestral estate while they continue undermining the Cult's activities in the Greek world together.

Disgusted by what the Cult had become as a result of Deimos' influence, Aspasia secretly helps the Eagle Bearer dismantle it, with hope that its original ideals of peace through order may survive.

The Eagle Bearer helps both sides of the conflict while also meeting and assisting Hermes Trismegistus, who offers to teach them about the Staff, and Hekate, who secretly seeks to undermine Persephone's rule and take over Elysium.

The Eagle Bearer eventually helps Adonis and his rebels to attack Persephone's palace, where they defeat Hermes in combat and confront the ruler.

After defeating Juno and Aita's latest creation, the Hecatoncheires, the Eagle Bearer deems Atlantis beyond saving and, alongside Poseidon, activates a mechanism to sink the city.

Now aware of the dangers of Isu artifacts, the Eagle Bearer accepts Aletheia's mission and leaves Greece to begin their new journey alongside Barnabas after gifting their spear to Herodotos.

Ancient Greece was one of the most requested regions by fans, and the era of the Peloponnesian War was chosen as the setting because it allowed the team to introduce well-known historical figures such as Socrates, Leonidas and Hippocrates.

[47] Three scouting groups accompanied by historians took more than 13,000 photos and videos during their field trip for research, and later the team made use of Google Street View to study Greek ruins.

[50] The team was influenced by other open world RPGs such as The Witcher 3: Wild Hunt, The Elder Scrolls V: Skyrim and Fallout, all of which give players a lot of freedom.

[76] The positive critical reception to Odyssey prompted Ubisoft to greenlight Immortals Fenyx Rising, which features various gods and monsters from Greek mythology.

[85] Additional costumes and ship lieutenants, including some based on previous protagonists of the series like Ezio Auditore, Evie Frye, and Bayek, were also released for free.

[101] IGN's Brandin Tyrrel described the in-game version of Greece as "a stunning series of picturesque locales," but remarked that occasional graphical hiccups may hinder the experience.

[98] While some reviewers enjoyed the scope of its world and the cohesiveness of its gameplay system,[93][97] Alex Navarro from Giant Bomb believed that the game was too repetitive and bloated with content.

[98] Joe Juba, writing for Game Informer, called the combat system in Odyssey his favourite in the series, praising the special abilities for conveying "a dynamic and godlike sense of power".

Juba liked the mercenary systems for creating a lot of intense combat situations, but he remarked that their continuous presence may also annoy the players, especially when they intervene during mainline quests.

[93] Although Messner felt that the story was disjointed and over-ambitious, he noted that the addition of choices added player agency and made the experience worthwhile.

The second part, titled "A Fated Encounter," is a crossover mission in Valhalla which explores the ties between the game's protagonist, Eivor Varinsdottir, and Kassandra as the canonical Eagle Bearer following the events of "Those Who Are Treasured".