According to Jesper Juul, Classic Game Model is what decides what is a game and what isn't a game. To be a game, there must be six criteria met:
1. A rule based formula system
2. Variable and quantifiable outcomes
3. Different outcomes are assigned different values
4. The player exerts effort in order to influence the outcome
5. The player feels emotionally attached to the outcome
6. The consequences of the activity are optional and negotiable.
In my belief, Mass Effect (specifically Mass Effect 3), meets all of these requirements in both the social and combat aspect of the game. First, the social system. The player (who plays as Commander <insert player's chosen name> Shepard) can interact with almost any non playable character, but more importantly, the members of the crew on Shepard's ship The Normandy. To interact with a person, Shepard must select them through whatever method their system allows and must make choices as to what they want their Shepard to say. The choices are on a wheel that has several responses, but the character can choose what type of attitude they want their Shepard to take. There can sometimes be dialogue options that can lead to "perfect" results. This can sometimes be the difference in life and death of certain characters, such as Urdnot Wrex in the picture.
To get these responses, the character's Paragon/Renegade score must be at a certain level. This can be influenced by the game's difficulty, alluding to the second criteria of what is and isn't a game. If some of the choices are not able to be selected, the outcomes can sometimes be disastrous. This alludes to the third and fourth level of the model. The game is written in such a way that even the idea of a character dying brings out great sadness. The idea that Shepard is responsible for these deaths? Shows the fifth aspect of the model. Finally, by allowing there to be different outcomes if you are a saint or a sinner, the sixth criteria is met.
In combat, the model exists much as it does in any third person shooter. If the player uses the fire button, the weapon will go off. The gun's damage can vary from weapon type, modifications, etc. Without ammo, the weapon cannot be fired. The gun can do varying amounts of damage, depending on type, modifications, and proximity.
All of these components lead up to the ultimate goal: The death/control/or synthesis of the Reapers.