My family plays Mexican Train often so my daughter loves playing with domino's. It makes her feel very successful when she can create long trains. She keeps telling me she is almost big enough to play with the grownups.
I have not taught her any game rules yet. I just give her the box of domino's and tell her to try and connect them all. I help her when she needs it but after a couple times of playing she is pretty independent and only wants help when she really gets stuck.
She does a lot of matching by color but some of them she does count to make sure she is matching them right. I have plans to start using domino's for different math games so I will post those game ideas as we play them.