The game's primary setting is a fantasy-themed alternate history Earth composed of a diverse blend of historical, cultural, allegorical, and mythological elements.

Atlantica Online is a turn-based tactical MMORPG in which the player primarily assumes the role of a descendant of the Atlantean people.

The primary goal of the game is to search for your ancestral home to save the world from the effects of Oriharukon, a substance created by the ancient Atlanteans.

As players journey through the world of Atlantica Online, their characters and mercenaries grow and develop, gaining access to new, more powerful skills and equipment along the way.

The rewards include experience points and loot like the game's virtual currency, various materials, pieces of equipment etc.

New decision impacts like the possibility to take cover, different height levels and the movement speed of specific characters are added while certain mechanics of the original combat system are removed.

Countries like Germany and China are represented, with cities like Munich, Moscow, and Sapporo as visitable hubs that offer services like banks, hospitals, the marketplace where players can trade goods with each other and other facilities.

Though the locations on the map feature climates similar to their real world counterparts, the architecture is often a generic recreation of well known structure types, such as the cities in Eastern Europe and Japan.

Most of the civilizations represented are anachronistic: Rome is set in the Holy Roman Empire, while Great Britain is independent, the Ottoman Empire reigns in Turkey, Southeast Asia resembles ancient Indian kingdoms before Western colonization and Islamic influence, and North America is caught up in the Industrial Revolution.

Updates include, for instance, new dungeons, quests, NPCs, skills, mercenaries, outfits, equipment, mounts, and community features.

Implemented in August 2010, the Troy Story Arc is a series of 'missions' following the format of the Tactical Battle System (TBS) that was introduced in the same patch.

This update was the most extensive to that date, introducing a new continent to explore (mythical Atlantis), new mercenary classes, new equipment, content and several changes to other features of the game.

Danny Gourley of Ten Ton Hammer praised its gameplay, stating that "it requires gamers to think a little instead of just mashing buttons".