Sure, playing is pretty clear, but what's "the majority"? Cutscenes can have a set time, but only the most limited games are set in the same way. For one player the majority of the game might be gameplay, but for a faster player the majority of the game might be cutscenes. And if the majority of it is cutscenes rather than playing, but it still has playing, what is it?

Back to the tangent:
I'd say "choose your own adventure" books are games, but obviously not video games. Choose-your-own-adventure eBooks would qualify as video games.

I feel that genres as they are have some value, but only because of what some of them actually are. They can be buzzwords for mechanics. We need a jargon/vernacular that describes established mechanics, and if it's a defining feature of a game we use it in its description. Jargon can be confusing, but genres are already jargon.

For example: FPS works fantastically as a genre because it's a simple joining of two mechanics: First-Person + Shooter. You might have a First-Person Explorer, or First-Person Driving Simulator, or Third-Person Shooter (although third-person needs better terms, because Third-Person could be interpreted as behind the player, over-head, shoulder-cam, smart-cam... these are all third-person). It's a connection of simple mechanics. A lot of driving games let the player choose the camera style, in which case it would no longer be a defining mechanic, and camera style wouldn't be mentioned.

MMO works similarly -- they used to be "MMORPGs", but these days the MMO prefix describes a mechanic of the game which can be appended onto others.

RPG is a genre, but not a mechanic, and it's pretty rubbish. It's a broad term that really refers to any game that demonstrates at least 5 of 17 different mechanics (intentional hyperbole -- I haven't actually counted out the staples of RPGs, but I'm sure you'll agree that there are enough that two RPGs could share none of the same mechanics and still be considered RPGs).

We should instead have well-recognised terms we can string together to describe the defining mechanics of a game. For example, you might describe a particular RPG as a conversational, indirect-combat (selecting actions to be performed rather than directly performing those actions; this would be as opposed to turn-based-combat [inherently indirect, making "indirect-combat" inherently real-time] and direct combat), smart-cam (Mario-style camera that follows loosely but is rarely directly controlled), grinding (earn experience through certain activities) fantasy game (actual style genres like fantasy and sci-fi still have their use).

Players who like RPGs only if they're allowed some twitch-action will know to avoid that game because of its indirect combat (probably a bad example -- it might make sense to stick just to turn-based and real-time as descriptors of action).