I've been playing Pokemon X again, to get some pokemon for a friend to help complete his collection, and I was struck again by a complaint of the series that I've actually harbored for a long time: that the RPG Leveling mechanics make the game intensely boring.
Basically, you can get a team of pokemon that 'work', and then as they level they scale to the (very very low) difficult of the game. While a player might change their pokemon team for any number of reasons, the game doesn't incentivize it as then you have to begin leveling a whole new pokemon that probably isn't up to snuff as your old ones, both in terms of level and the carefully sculpted movesets that the ones you've been dedicating your time to have.
So I've thought about it, and I think it'd be cool to have a pokemon-style game where your monsters don't level up. They just have flat strengths and weakness, set abilities, territorial bonuses, type advantages, things like that to differentiate them, so that progressing through the game isn't a matter of picking up your Charizard and smashing him into every obstacle the game throws at you, but rather a puzzle that requires careful thought and planning about your team composition versus enemies plus territory. Obviously the balancing and pacing of the game would have to be WAY WAY WAY different from pokemon, but that's the gist of it.