My sifu always reminded me that you can tell the quality of one's gung fu by the age he passes away at.
Since Gung Fu is an individual endeavor, what makes gung fu ...gung fu is the INDIVIDUAL and the hard work he puts into it. Sure, gung fu mean great skill developed through hard work over time. But, gung fu isn't just about martial arts. Gung Fu is SKILL any way you look at it. Gung Fu can be found in any art, any sport, and THING an individual who puts in the time and effort to be good at what he or she does.
Long ago, i heard a Chinese Chef being called "SIFU" and i asked my sifu "is he a martial artist?" My sifu informed me that yes a CHEF, an athlete, a painter, or even a dancer or even a tattoo artist who is at the top of their game can be called Sifu and said to have good gung fu ....meaning skill.
So, on the most important level, what makes gung fu ....gung fu is HARD WORK by the INDIVIDUAL.
Where i believe a problem lies is when people try to imitate the CHINA side of chinese martial arts. Some will try to "BECOME" chinese just to be accepted by the Chinese. Others are intoxicated by the vapors of gung fu and completely misconstrue the art and get all esoteric and mystical. THAT is not gung fu. Chi is not exclusively "GUNG FU" because Chi can be built up by any athlete not related to gung fu.
So whether you're interested in weapons, forms, lion dancing, or fighting, if you don't put in the work you will never have good gung fu.
JUST MY OPINION.