yeah, the type of game where you don't do anything except 1 vs 1, 3v3, and 5v5 (and 10v10 for some). But if you aren't giving Visual Novels their own genre then MOBA arguably shouldn't be either.
I've skimmed over most of the stuff others are posting, and it still seems like things are getting over complicated. If you use the term 'platformer' to describe the main gameplay style - as in there's a heavy emphasis on you jumping on platforms, yet want to differentiate between 2D and 3D, between ones with lives and ones with checkpoints, it seems like you're not really trying to achieve the simplest form of labelling.
Things like the Tower Defence you mentioned. It's a strategy game, which is played in real time. Therefore you'd simply use 'strategy' (since real-time is the norm). If it were turn-based, then it'd be 'strategy' + 'turn-based'. Again with the GTA vs Zelda thing - if you're going for the simplest way of defining them, then the level of freedom you're granted should not come into it, nor how you go about it, as you then get into guns vs swords, experience vs expansions (for health and stuff), on foot vs in vehicles, single world vs overworld + dungeons, etc.
the problem with doing strategy + turn-baseed is that "turn-based" by itself isn't a genre and i'm trying to make a list of genres that can stand alone.
i'm also not necessarily going with the simplest way of defining games - in that case every game's genre would be interactive fiction. it's more like what's the simplest way of defining a game's genre so that if someone looked at at the genre, they'd get a pretty good idea of what the game is like. i don't think calling gta an "action/adventure" game would do that, but "action/sandbox" certainly would.
with only 2 genres, a lot of games don't fit, as i said, rune factory and disaster can't be defined by only 2 genres...
well, now that i think about, if you could define these types of games with something like "this game is comprised of various snippets of genres" and then you could use the other one to define the general genre of the game...
then rune factory would be adventure while disaster would prolly be survival or action...
disaster have a absurd amount of different types of gameplay, you have 3 parts where you race against something, you have on-rails parts, adventure parts and survival parts....
rune factory have the whole farm simulation, plus adventure parts (inside the dungeons), dating sim gameplay and a RPG system.
disaster have a absurd amount of different types of gameplay, you have 3 parts where you race against something, you have on-rails parts, adventure parts and survival parts....
Lots of games have elements of different genres tossed in somewhere. What you're looking for when assigning it a genre is what the primary element is. I don't count Ocarina of Time as a racing game despite the inclusion of races or a puzzle game due to the puzzles dungeons tend to have because those aren't the focus of the game and not what you spend most of your time doing. If you're going to try and fit a game into every possible genre it could possibly have you're missing the point.