Defining the Sub Generas

Nobody really cares anymore which games created or made popular a core genera.  For instance, when was the last time someone said, that game plays like Dune or that game played like Wolfenstein.  No, we just say its a RTS or FPS respectively. 

However, sub-generas are very different.  In many ways, we still don't have true containers to put them in, so we continue to compare to a particular game.  Else we just slap it with the meaningless label 'Action' game. Here are a few games that have made a particular type of sub-genera popular (for better or for worse).

Plays like... Gears Of War
This classification indicates a 3rd person shooter, practically on rails.  You run and gun, a tank with legs.  Collect meaningless shit, see lots of explosions, and sleep through the plot.
Games in this Family: Warhammer 40k: Space Marine ; Transformers: War for Cybertron.

Plays like...Doom
This classification indicates its a throwback to the classic FPS days, where nothing mattered accept staying alive and killing cool things animated in front of your reticle.
Games in this Family: Serious Sam ; Painkiller ; Hard Reset.

Plays like... Borderlands
This classification indicates a multiplayer coop shooter with meaningless RPG elements tossed in.  You can randomly pick pieces from the "progress tree" and the game will still play the same.  Expect senseless side missions, with a dash of real plot in the main storyline.
Games in this Family: Dead Island ; Brink

Plays like... Call of Duty
This type of game is a shooter, mostly FPS. Generally will have lots of explosions, waves of enemies that won't stop unless you move forward, pretty graphics, and utilize the wait and heal mechanic.  Plot is generally over-the-top filler, designed for kids that missed out on growing up to Stallone and Schwarzenegger on the big screen.
Games in this Family: Homefront ; Halo

Plays like... Tomb Raider
For this, your jumping from cliff to cliff, roof top to roof top, generally in the third person perspective.  Snobs like to use the word: parkour.  When your not fighting the camera angles, you'll be collecting stupid crap for an 'Achievement', while shooting waves of stupid AI enemies that seem to be wrestling with the same camera problems.  If you survive, you'll be graced with a cut-scene that will progress a storyline that's reminiscent of your favorite action movie.  Game requirement: must have some type of Sci-Fi twist.
Games in this Family: Prince Of Persia ; Assassin's Creed ; Uncharted

Plays like...GTA
That's Grand Theft Auto III specifically.  Indicates you'll be in a open world, full of unlimited opportunities to do stuff, approach objectives from different angles, and most importantly, add many elements without the distraction of monotony.
Games in this Family: Far Cry 2 ; Red Dead Redemption

Plays like... Farmville
This classification indicates you'll be spending a good chunk of your time doing meaningless repetitive tasks, all while telling others how cool it is, and how they need to do it too.  Meanwhile, your plant just died of thirst, and you just made somebody you never met, very rich off your stupidity and loneliness.  Micro-transactions a must.
Games in this Family: Age of Empires:Online, World of Warcraft, Mafia Wars.  Any modern game that claims to be free.