I think it leaves behind a pretty decent legacy, albeit one that is pretty well worn and leaky. The biggest attribute would be that it was featured on the Evo stage two years in a row, which is more than many games in the past have, so props to that, and while the first Evo was unfortunately during a time when the game's meta was very 1-dimensional and a bit plain to watch, the second Evo did not disappoint in excitement and epic matches. Even the first Evo, ignoring the early game slop, was entertaining and had its own fair share of upsets and storylines. A B- showing at Evo 2013 and a solid A at Evo 2014 I'd say.
There was a lot of new players that came to prominence and some old MK hands who stepped up to the majors, which was great to see. People like Honeybee, Whiteboi, Theo and Jupiter, who had minor MK appearances at best, became established names, with Theo taking three of 2014's biggest tournaments and Jupiter and Bee remaining pretty prominent top 3 placers all along the East Coast. MK hands like Pimpimjim and Noobe achieved some of the highest marks in their career in Injustice, and even the old top guys like 16 Bit, DJT and ForeverKing stayed relevant throughout the game's life.
As much good as there was, there was plenty of rough patches to go through. Number 1 had to be the false narratives and disingenuity that ran rampant early in the game's life and that still persist even to this day. Notice how Dave keeps spamming that scrubs got DS nerfed, when by the time the first patch came out that nerfed gunshots there was no possible way they could have gotten two weeks of feedback and had a patch approved by MS. There are countless other examples, chief among them the Scorpion drama in which certain players winning was seen as unacceptable and a massive witch hunt commenced. Another big issue was the overreaction to seeding, or particularly the lack of at first posting. Seeding is an important thing, but the massive amounts of butthurt when pools are initially posted is an embarrassment and all those who contributed to that should apologize (preferably on their knees).
Bitterness, in and of itself, was a huge issue in general. Whether it was old MK players who couldn't cut the mustard or new players looking for an excuse, or even IGAU players desperately seeking approval, the amount of funny walking caused by large, inanimate objects being shoved up rear ends was a sight to behold. I will say that for the most part this was a forum only issue, as tournaments were always fun and most of the biggest babies stuck to TYM. Mostly.
Lastly, the self bashing of the community itself got really bad. Old grudges and soft feelings came to the forefront and caused many a forum goer to bemoan the loss of the community spirit, which was so ridiculous I can't imagine anyone typed it with a straight face. Egos colliding is the forefront of any competitive activity, and while people get heated, it's not a reason to start shaming the community as bullies and jerks because of it. My hope is that by the time Mortal Kombat X comes around a lot of people toughen up and understand that people want to win and like to have fun, so yeah, there may be a little name calling and some flare-ups, but that doesn't mean we all need to get red fist avatars and "save the community" from itself.
All in all, a decent game.