Gambling consists of three elements – prize, chance, and consideration. Here is the link to an article on an interesting decision recently made by an intermediate court in Pennsylvania. The court concluded that a video poker machine was a game of skill after removal of the random number generator and modification to the play button.
A majority of states apply the Dominant Factor Test in determining whether an activity is gambling. Basically, courts will look at whether skill or chance plays a predominant part in the activity. If it is chance, then it is gambling. There are some activities that can be argued as being dominated by skill, such as poker, but, like in Nevada, are statutorily deemed a gambling game anyway.