An easy way to beat Goro in MK4 is to use the spiked club from Reiko or Jax. Do the high punch attack (when they hit the enemy into the background) run back there to Goro, and do it again as soon as he gets up! Repeat until dead. If you get MAXDAM, just run back again after you are knocked away. He may block it sometimes, but just keep trying it.
The hardest boss for me was definitely Kintaro. The only way I could beat him was with Kitana doing the fan lift over and over.