While various features of gameplay varied across the series, the Mass Effect games are action role-playing games. The player customizes their version of the game's main character (Shepard for the first three games, and Ryder for Mass Effect: Andromeda) based on physical appearance, background, and one of six character classes, each class centered around one or two specializations in combat, technology, or "biotic" (magic-like) skills. This establishes a skill tree that the player can advance through as their character gains experience levels through completing missions. Each game generally follows a main story pathway with points of branching narratives and multiple side missions, allowing the player to proceed through the game as they desire. Both story and optional missions most often involve using their ship to travel via the mass relay to remote star systems and explore planets to find target objectives.
When exploring planets, the player has the option to bring up to two of their crew members with them, who generally act autonomously but can be given specific orders by the player. In missions, the player can explore an area to find information, discover lootable objects with new gear or in-game currency, non-playable characters to talk to, and key mission items that are to be recovered. Frequently, the player will enter combat, which plays out as a third-person shooter, with the player and their allies using a combination of their weapons and combat, tech, and biotic powers along with tactic use of the environment to defeat opponents. There are five different types of weapons: assault rifles, sniper rifles, shotguns, pistols, and in later games, heavy weapons (i.e. grenade launchers, rocket launchers, flamethrowers, or heavy machine guns). Due to these weapons being collapsible for easy storage, it is possible for a player to carry all five weapons at once and alternate between them depending on their position, enemy type, and situation. Melee weapons include fists, the butt of a gun, or in later games, a condensed holographic dagger called an Omni-blade.
Through story encounters and missions, the player meets a number of non-player characters and engages in dialogue trees with them to learn information and progress the story. This is presented through what BioWare called a Dialogue Wheel, with the player-character reply options shown as choices extending radially outward from a circle at the bottom of the screen. Most of these choices are simple questions and responses, but in some dialogues, they offer additional choices that either influence how the game plays out from there, or are as a result from those previous choices. In the first three games, these choices influenced the player-character's morality, putting them on the path of a Paragon or Renegade, indicated by color and positioning on the Dialogue Wheel. With the second and third game, it became possible to select these choices during the non-player's character dialog, resulting in an interruption of the action that could have even larger ramifications. The player's choices of Paragon or Renegade could change how some parts of the story progressed and could limit choices of allies they could gain later in the game or the ability to access powerful gear. Cinematic designer John Ebenger stated in 2020 that only about 8% of the players chose the Renegade route across the first three games, and jokingly lamented about the amount of effort they had put into some of the Renegade cinematics.[3] In Andromeda, BioWare replaced the Paragon/Renegade distinctions, which were tied more to the Shepard character, to a new system based on four ideals of emotional, logical, casual, and professional attitudes.[4]
Among notable side missions in the series include the various romancing options with the main character's crewmates: these included both hetero- and homosexual relationships since the player-character's gender was selectable, as well as intra-species options. Players could work to improve their relationship with these characters through dialogue options, providing them gifts, or completing various side missions specific to each character. Successfully romancing a character would typically lead to scenes leading up to a sexual encounter though otherwise not showing anything inappropriate for the game's rating. These options had created some controversy for the first game on release with mainstream reporters critical of the sexual content of the game.