Sorry for the word salad, but I always find it cool when games let you play other games within the world of the game. Like how in Shenmue, you can play Space Harrier and Hang-On at the arcade (and even acquire copies of the games to play at home on Ryo's Saturn). Or in the first Black Ops, you can play Zork.
What are other cool examples of this you can think of?
What are other cool examples of this you can think of?