Any thing NOT close to Mortal Kombat ( Way to massacre a great gaming genre, Midway...literally.)
In my opinion, a good Fighting game needs balance. Enough for each character to have pros and cons over each other, but not to the point where each are basically clones of each other, in different costumes. Some games suffer from over powered characters***cough**Ryu*Ken*Akuma*KOF bosses*** that make it damn near impossible for the really unique characters to even pose a challenge.
Intricate combos, and versatility to use and mix them with other signature moves, are definitely key. No button mashers though. But not too precise, where game play feels stiff.
Interactive backgrounds, that literally make or break a characters preset game plan or strategy. I'm not talking shitty break away objects that are just fixture, or eye candy. I'm talking, textures that slow the quickest character down, to make him rethink his machine gun tactics, or confined areas that force larger characters stray away from the poking game. Down hill, uphill, gravity, FUKKIN' physics, here people.
And for craps sake, a BELIEVABLE STORY LINE!!!! Far too long, I've been reading and seeing these fictional stories, that practically become ridiculous by the end of it's run. And please...stop with the anime, already. Why not adopt a new art style, for a change?
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I just basically gave you a run down of what MY fictional fighting game is practically about. Though at the moment, I'm still building on the story portion, as it's utterly farked, plot-wise(trying to interwine as best as possible.) There's more, and I could go on, but it's past my beddy time...plus I'm trying to actually finish a big pixel art piece for once. (trying to go it alone, without any critiques as an experiment...)