Adding to Gregg's comment for better defining the "challenge" associated with ethical, honest, respectful, law abiding hunting as it applies from the dictionary definition of challenge-
"The difficulty in an undertaking that is stimulating to one engaging in it." Thats the challenge of hunting to me. I am not competing with other hunters for a competitive goal or a defined prize putting the end before the means but only answering the challenge within myself. The stimulation and interest can be defined as excitement, satisfaction or whatever. Regardless of the recreational activity you engage in, if its not stimulating or somewhat exciting (i.e. Challenging) you will tire of it and lose interest.