Injustice was a special time.. It brought a lot of new players to the scene, as well as marked a coming of age of some guys that had played MK9 but not really made their mark.
We had:
Theo
Slayer (greatly improved although he was active in MK9)
Max
Whiteboi
KDZ
Ducky (greatly improved over MK9)
Jupiter
Honeybee and Bio
Orochi
Filipinoman
Oxygen
Sonic Fox (who we knew was good in MK9, but hadn't reached his "world dominating" level yet
Rico Suave
Digit
Grr
SaltFace
Deg
I mean, this isn't even a full list. Massive infusion of new and developing blood into the scene. Also, the rivalries were particularly bitter because a lot of people felt they had something to prove after MK9. So the whole returning cast of 16 Bit, REO, Noobe, Pig, Cowboy, Vegas etc. thrown into this mix of new people was fun to watch.
We also had WNF, GGA GBS, NLBC, ATL/Scraps and The Break weekly streams, which was the best period of time for weekly tournaments and streams we've ever had.
MKX is hype in its own way though. I think the biggest change has been the consistent presence of the game's top players at every event. Before, you had to guess who was best nationally, before everyone came together at the "big" majors and duked it out. Now, you get to see a top level of play at almost every event, which is something I appreciate. ESL has also helped people travel, including international players we'd never get to see. Seeing Foxy vs. Sonic Fox is cool.
Yes it's mainly the same top players we already knew (sans Dragon), but people have become much better players over time, and the level of understanding of fighting games is much higher than it was in MK9.
I guess different strokes for different folks, but I've enjoyed both games and the different things they bring. And who knows what'll happen before EVO this year. Still a lot of road ahead!