The Essence of chess
Fundamentally, chess is a turn-based logic game. Each player gets to move one piece after the other has finished, hence the “turn-based” part. The “logic game” part implies that there is a finite set of legal options at each stage in the game, in this case defined by simplistic rules restricting the movement of pieces. The complexity of any logic game - and thereby also chess - arrises from the long sequences of moves that are required to win the game. Therein lies the challenge: a player, whether human or artificial, needs the ability to deliberate over the best sequence of moves that will ultimately win the game.
Generally, the ability of deliberative thought is associated with intelligence, hence the stereotype linking chess with brainy people and as the main challenge of A.I. There's little doubt in my mind that deliberative reasoning is one of the components of intelligence, none the less it does not remain its only requirement!