In the game, the player must resolve a murder mystery by searching for clues, exploring different areas, interacting with characters, and solving item-based puzzles.

It became an influential title, helping to define the visual novel genre as well as inspiring Japanese game designers such as Hideo Kojima and Eiji Aonuma.

[1] It features a conversation system with branching dialogue choices, where the story develops through entering commands and receiving answers to them from the player's sidekick or non-player characters.

[6] This includes travelling between different areas in an open world and making choices that determine the dialogues and order of events as well as alternative endings depending on who the player identifies as the culprit.

[1][4] The Famicom version of Portopia also features branching menu selections, which includes using the pointer as a magnifying glass to investigate objects, which is needed to find hidden clues, and as a fist or hammer to hit anything or anyone, which could be used to carry out beatings during suspect interrogations.

[1] The president of a successful bank company, Kouzou Yamakawa (山川耕造), is found dead by his secretary Fumie Sawaki (さわき ふみえ) inside a locked room in his mansion.

[10] The detective in charge of the case is an unnamed, unseen and silent protagonist who essentially embodies the player, and is simply referred to as Boss (ボス).

[1] Other characters include, among others, Yukiko (ゆきこ), daughter of a man named Hirata (ひらた); Toshiyuki (としゆき), Kouzou's nephew and heir;[10] and Okoi (おこい), a dancer.

[2] This version of Portopia changed the interface, adopting the command menu system that Horii created for the 1984 adventure game The Hokkaido Serial Murder Case: The Okhotsk Disappearance [ja].

Due to frustration with text-based entry, admitting he was never able to get very far in adventure games because of it, Horii created a command menu system for Hokkaido, which was later used in the Famicom version of Portopia.

[1][9] The game was never released in the Western world, largely due to its mature content, involving themes such as murder, suicide, fraud, bankruptcy, interrogation beatings, drug dealings, and a strip club.

He praised Portopia for its mystery, drama, humor, 3D dungeons, for providing a proper background and explanation behind the murderer's motives, and expanding the potential of video games.

[20][4] Portopia was also one of the first video games ever played by Nintendo's Eiji Aonuma, who went on to become the director of The Legend of Zelda series starting with Ocarina of Time.

[2] He noted that it contains elements found in a number of later titles, including Déjà Vu, Snatcher, 428: Shibuya Scramble, and Nine Hours, Nine Persons, Nine Doors.

[26] According to Official Xbox Magazine, Portopia's features, such as point-and-click, murder mystery plot, open world, suspect interrogations, nonlinear gameplay, dialogue choices, and alternate endings, are "standard for 2015, but way ahead of its time in 1983", comparing it to L.A.

[4] Peter Tieryas gave Portopia a positive retrospective review, stating that, while its "influence is undeniable, it's the tragic back story, the strange vicissitudes the characters face, the uncanny freedom to investigate, and the haunting uncovering of the killer that makes it so special.