MK is one of the greatest fighters to have ever graced arcade and console alike.
On one hand, it's a helluva lot of fun to play. The blood, the gore and the sheer awesomeness ofallmost of the characters come together to make a game that you can't put down.
On the other hand, the fighting engine isn't as deep or complex as pretty much all the 3D fighters available right now (Tekken and Soul Calibur really kick several shades of brown out it. Even the lesser 3Ders like Dead or Alive and Virtua Fighter are easily more in depth). And in the 2D arena, nothing can really stand up to KoF.