It is half empty. The answer has nothing to do with me being a negative person or how I see the world or any of that nonsense. The truth of the matter is that someone poured the glass full at one point, Not Half Full (why would anyone fill a glass half full). THEN the glass was emptied to the point of half.
So, the owner of the glass at this point can either exhaust or empty the remaining contents OR request a refill of what he/she is missing, but either way the owner is lacking the first half - half empty is the answer.