Street fighter 2 was the spark, Mortal kombat 2 was the gas that set the fire in Beat 'em ups.
First of all many chosable characters for it's time (12), moreover it included 2 female fighters (a fetish of mine). The characters were real actors and not drawings.
Furthermore MK2 like MK1 introduced a whole new way of beat 'em up games. It no longer is the traditional game, now it features many different moves for every character, Fatalities, Friendships, secret characters and some story other than "revenge the death of someone you loved".
Graphics were very nice for it's time and the abilities of AMIGA, sound was very nice also, and finally the characters were fantastic.
Absence of Sonya was a huge disappointment for me, what the heck, they could have kept the original characters and add some more.
Anyway there are some minor annoying things:
Babalities, they were adding nothing to the game (by the way all of them were the same)
The ugly face appearing after an uppercut and his comment (I understand the need for promotion of themselves - the authors - but this was really annoying)
Finally the one fire button (but AMIGA had only one), Using keyboard if desired would be very nice.
The Bottom Line
Finally to add a point that is evenly good and bad, is the extra game of breaking things, nice for a variety but away from the plot.
I would describe it as the game that really changed Beat 'em up scenery in it's time.
Rates for it's time and AMIGA's capabilities