Mathematicians rate the complexity of games by the size of the tree of lines that can be played from the initial position. On this basis, go is the hardest followed by shogi, xiangqi, then chess, and finally checkers.
Games like bridge, dominos and snap are usually classed as games of chance because much depend on the cards or dominos you are dealt. They are not complex so much as based on luck.


well as Mae West used to say. "A hard game is good to find"......Just thinking outloud here.