There was a time when this was the most popular game going, because there was nothing similar to be found: copious amounts of blood, "fatalities," real-life character models. This was the game that opened the floodgates for ultra-violent videogames, for better or worse. The Sega Genesis version is pretty faithful to the arcade. The graphics and sound are pretty ugly but then the coin-op never looked too good to me either. And unlike the cleaned-up Super Nintendo version, all the blood and guts are there, a point which I remember being an issue back in the day. A lot of people used to say that they'd rather have the Genesis version than the SNES, because despite the somewhat better graphics of the latter, the SNES version had all the blood taken out.
Overall, I think Mortal Kombat for the Genesis is a pretty damn good home conversion, especially given the limitations of 16-bit machines.