I pose this question, since I have watched many of William Lane Craig's great academy award winning performances. I have heard many atheist say that he has won most of the debates against atheist, but I have always come to the conclusion that he has not provided anything with substance. He uses the same old arguments that are known not to be very strong. Therefore from my point of view he lost. I think a person wins a debate if their claims are true, if they provide evidence, and if the arguments are strong. A weak argument that has been adorned does not meet my standards.
I have heard people say that Craig has won the debate because "X argument" was not rebutted, but if there is not enough time to shut down every single argument he proposes (which are about 5). How can that be considered a lost for his opponents?
Craig tries to make an argument for a creator ( the kalam cosmological argument), and then extrapolates that argument to apply to the christian god (but never saying it explicitly, unless he is pressed). If that argument can apply to many other deities, than how can it be considered a winning blow? It is a weak argument. Also, I consider the exploitation of the debate format for those purposes to be intellectually dishonest.
In short, what determines that you have won the debate?
Is it the exploitation of the debate format?
Is it the truth of the claims or the strength of the argument?
Is it that the other side is unable to answer convincingly even if the argument proposed is weak?
Most people will say "oh well is a combination of all those aspect", but to me the strength and logic behind the argument trumps all the other aspect of a debate.