The thing about genre is it tells you relativity nothing about the game itself, look at two mainstream FPS, Call of Duty and Halo. The games are the same genre, have a mostly shared audience but the games themselves have almost nothing in common: COD has guns based on real weapon models, Halo doesn't; Halo is set in the distant future, COD isn't. So what does genre really tell us, well they are both in the first person perspective and feature shooting stuff, but even the shooting is different. COD features iron sights, a realistic approach to aiming where you hold down a button to look down the sights and aim, where Halo features a more classic 'from the hip' approach to aiming found in old fashion shooters like Doom. But even those traits are quantifiable (meaning you can describe them in a manor that can be taken as fact), still other differences between the two games include graphics, physics and countless other software differences; as well as opinions like personal preference and overall playability.
Yesterday I made a new genre, adventure-sandbox, and I created this genre to deal with the vague genre of action-adventure. But even this much more specific step leaves a lot of room for interpretation.
Two major adventure-sandboxes, Assassins' Creed and Red Dead Redemption; they have a ton in common, same objective system, similar exploration system, but when you look at the combat and movement systems the games couldn't be more different. Red Dead is a third person shooter with bullet time and a movement system based around tapping the A button (or X I'm an Xbox guy remember) to move faster. Assassins' Creed however is a hack 'n slash (with only one button for attack though, most games of this type feature two attack buttons for fast and strong attacks) with an emphasis on combat awareness, counter attacks and surprise. The movement system features a 3 gear system, slow if you just walk, quick if you walk and hold the trigger, and fast if you walk, hold the trigger and press a button. These differences are major but they don't 'break' the genre; adventure-sandbox games don't all have to have the exact same attack or movement systems as long as it occurs in a sandbox and follows an adventure. But this discrepancy becomes a bigger deal when you really enjoyed Assassins' Creed so you try out Red Dead because they are the same genre; however you really dislike shooters and can't enjoy the game because of its combat system.
Tomorrow we'll continue this discussion and delve deeper into Assassins' Creed especially to find the core issue with genre.