It means you look good. Girls need to calm down and stop trying to over analyze everything that guys say. Unlike girls, guys just say what they mean/feel. We don't disguise anything or beat around the bush. Why didn't he say pretty/cute/beautiful? Who knows. Perhaps for him "good looking" means something better than all of those words. No one can read his mind.
Guys trade out words and to us they mean the same thing. good looking, cute, pretty, beautiful, etc. We don't ponder what each one means in the context, we just say what comes to mind. Try to get the overall meaning instead of deciphering each chosen word. He paid you a compliment.
My question is... what did you say after he told you that?