Gameplay in Mass Effect 3 will be influenced by decisions from Mass Effect and Mass Effect 2 and have settings throughout the galaxy, including Earth and Mars. Combat has been changed and refined; in particular, the cover system has been improved, there will be more options for moving around the battlefield, instant melee kills and more conventional grenades will be introduced as well as improved artificial intelligence. A four player multiplayer co-op mode will also be available.
Mass Effect 3 will follow from the events of the Mass Effect 2 DLC expansion Arrival and follows Commander Shepard's mission to save the galaxy from the Reapers by rallying civilizations of the galaxy together, while also having to deal with Cerberus, who have decided to turn against him/her.
Players with saved files from Mass Effect and Mass Effect 2 will be given the option of importing them into Mass Effect 3. If a saved file is imported, over 1,000 variables will be pulled that will help shape how the final chapter is experienced. If there are no saved files available, there will be no origin-story comic for new players to help them make quick decisions like there was in Mass Effect 2. Imported characters' appearance and class will be changeable, with more features and hair-styles included in the character creator than in Mass Effect 2. Commander Shepard will always start the game with some powers. Upon finishing the game, there will be a New Game+ option that allows players to continue playing after the main story ends or start again with their finished Shepard and collect items they missed the first time around. The game will have 82 minutes of cut-scenes.
Mass Effect 3 will have three pre-set campaign modes: Action Mode, Story Mode, and RPG Mode. In Action Mode, conversations will have automatic replies and a normal combat difficulty. In Story Mode, conversations will have manual replies and a minimal combat difficulty. In RPG Mode, conversations will have manual replies and a normal combat difficulty. This last mode is reflective of the typical Mass Effect series experience. Overall,the RPG elements in the game have been improved over those in Mass Effect 2, with a more detailed leveling up system and increased weapon customization. To level up characters, players will have skills that start along a single path and then eventually splinter into two branches where they can select only one upgrade or the other along a sequence of possibilities Players will also be able to customize their weapons with different scopes, mods, barrels and ammo types. There will be 25 weapon mods total — five per weapon type — and each of them will have multiple power levels to collect. The game will include mini-games (although planet scanning is unlikely to return) and Hammerhead and Mako missions. To select dialog options, players can use Kinect to speak their choices instead of selecting them with a controller.
As of August 23, 2011, BioWare has confirmed the return of previous characters Liara T'Soni, Kaidan Alenko or Ashley Williams, Miranda Lawson, the Illusive Man, Garrus Vakarian, Legion, Massani, Kasumi Goto, Kelly Chambers, Thane Krios, Jacob Taylor and Ambassador Donnell Udina from Mass Effect and Mass Effect 2. Some characters will not return if they were killed at any point during the previous games. The number of characters available as permanent squad mates will be smaller than in Mass Effect 2 for the purposes of deeper relationships and more interesting interplay, including same-sex relationship options for both male and female Shepards. If players achieved a love interest in both Mass Effect and Mass Effect 2.