Genres are a way of describing the gameplay of a game, in an efficient manner.
here are some examples.
Platform - originally consisting of your character jumping from platform to platform ala Mario. Though now-a-days it basically means any action game featuring a stylized character. Crash Bandicoot, Jak and Daxter and of course Mario.
Action - not so much a genre in itself. However it used as a descriptor for other genres, Action RPG, etc.
Roleplaying - any game where you assume the role of a character in a plot, generally accruing experience which you use to upgrade your characters abilities. Example games would be Final Fantasy, Dragonquest and Ultima. I used to have issues applying the RPG moniker to games like Diablo which have a large emphasis on action, but Action RPG, is a perfect way of describing them.
First Person Shooter first person shooters are any game that you control from a first person perspective, usually using all manner of firepower to make your way from A to B. This genre has changed a lot since its inception with Wolfeinstein/Ultima Underworld. Adding elements from other genres such as RPGs and even sports titles. Quake, Unreal, and Halo are prime examples of this ever evolving genre.
What about everyone’s favorite genre created by Grand theft Auto? GTA spawned a genre that has changed gaming more than any other one. Yet, it still doesn’t really have a uniform name.
Its been called Sandbox gameplay, but that isn’t really accurate, and does a disservice to the genre, sure you can do anything you want, but there are goals and requirements which you would surely fail.
Its been called Open World, but I dont think that is an accurate term either, because again, it only centers on a single element of the genre, that being you can go anywhere. Surely other games would have done this, had the technology allowed it.
That is why I propose that we universally call the genre Free Roaming Action. It does a good job of quickly summarizing the gameplay that games like GTA, Saints row, and Just Cause have so successfully exploited.
With all of this confusion, why have Genre’s at all? word of mouth for one. You can not rely on the eloquence of your customer to get point across. Not to mention publishers generally like to hear how your game compares to other games in the same genre. It also gives people an immediate and clear impression of your game for whether that be for better… or for worse.