Ah the joys of computer game sequels. Like most sequels, Mortal Kombat II was basically like Mortal Kombat – with a few tweaks and enhancements. Mortal Kombat II has Shang Tsung, the bad guy mastermind from Mortal Kombat as one of the fighters – which is kind of fun.
The technical differences in Mortal Kombat II include a lot of graphical cleanup (the characters no longer look like cardboard cut outs on a computer generated background) and the addition of ‘babalities’ (where you turn your opponent into a baby) and ‘friendships’ (where rather than killing your opponent you spare their life). Frankly I prefer the fatalities over these two.
Mortal Kombat II also added a number of arenas which you could interact with, and uppercut your opponent off the stage, or push them into spikes / acid / etc…
All in all a lot of fun. For more details checkout: http://en.wikipedia.org/wiki/Mortal_Kombat_II