I was VERY impressed when Metris came out and i'm hopeing stefan will add more mini game NPCWs sence you can play it when you are waiting for some 1 and it can be used in event sence you say your score when you stop playing it i got some ideas too
Pac-Bomy! - Pacman
Graal Invaders! - Space invaders/Galaga
Cardgames - Blackjack poker hearts ect..
Dragon Attack - you get to be a dragon and blow up towns like godzilla
are all i can think of right now
but you can put them in a shop sell them for like 50-150g so they are not all free or add some kinda mutli player mini games like pong or something....