Killer Instinct isn't finished yet. It's an attempt to get players to buy into a promise that the full game is still on the way, that investing now will guarantee an experience on par with other fighting games – eventually.
Right now, there's little else aside from training, survival and online modes. There isn't a story mode or an arcade mode, though the latter is promised for the future. There are only six fighters, with two more to come during the game's first season of content. As it stands, Killer Instinct is a streamlined fighter designed as a far-reaching modular experience, which highlights one of its key problems: a dearth of content.