Mass Effect 3 is the final part of the trilogy of the same name, created by BioWare. It is an action RPG with wide customization opportunities and several endings that depend on your choices during the game. There are side quests you can complete, and a relationship system that opens new ways to fulfill tasks and lets to romance some characters. The game follows traditions of the cosmic opera genre and features interstellar travel, space fights, and interaction with various alien races. Mass Effect 3 heavily focuses on combat; the core is shooting with a cover system and pursuits.
You play as Commander Shepard (who can rather be male or female) during his fight against the race of Reapers, that invades Earth. The only hope of the world is the absolute weapon you have to create with the help of all races. The tone of the series switched to more pessimistic compared to previous games. Your actions may lead to the deaths of your friends, and this makes your choices harder. 
The game is followed by Mass Effect: Andromeda, however, this installment is not a direct sequel to the trilogy and follows the story of brand new characters.