Let's not beat around the bush.  The only  reason the Mortal Kombat series has been so successful is because of the fatalities.

Where other fighting games were content to just let your opponent be defeated, Mortal Kombat took versus gameplay a step further and made it personal.  When you beat someone, you were given a chance to finish the job - to actually kill their character - as a bit of punctuation.  Other games quickly followed suit (with mixed success), but Mortal Kombat was the original and best, and has remained so to this day.

Here you will find videos of the various finishing moves (Fatalities, Babalities, Animalities, etc,) from the Mortal Kombat series.  Relive the joy of Sub-Zero's infamous spine tearing fatality from the original Mortal Kombat.  Ooh and aah at the sheert brutal goodness of Scorpion's ultra-personal fatality from Deception.

In addition, each fatality has been given a rating in each of the following five categories:

Execution - Was the fatality a good concept?  Was it well executed?

Gore - The bloodier the better.  Dismemberments are also a plus.

Brutality - Anyone can kill someone, but a really brutal fatality makes it seem much more personal.

Effectiveness - Does the fatality ensure that they are indeed dead?

Satisfaction - best measured by the smug look on your face when the fatality is over, and comparing it to how angry your friend (who just lost) looks.