I’m going to interpret this as asking for a kind of Platonic ideal game, as we’ve already talked about favourite games.
The perfect game for me would be a simple system (no more than 20 pages of rules, total) with abstract measurements for your characters, and a single mechanic that addresses any kind of conflict resolution. I don’t want to be rolling too many dice, but I definitely want dice to be rolled. Give the player plenty of narrative input and make creating mechanical obstacles so easy the GM can do it on the fly with a minimum of brain power.
This is the game I am always trying to design. This is the game I always want to play.
#RPGaDAY2015 is the brainchild of game designer Dave Chapman. Basically, each day in August there is a question about RPGs.