Incentivize game development by letting the community vote with wallets and play time (see Free Market).
Creating games is easy... creating engaging experiences with replayability and lead to the recruitment of new players is the challenge.
Incentivize this achievement amongst developers by using existing metrics and exploring new ones.
Existing: Play time. Play preference (is it the first game they play when they put on the headset). Store Rating. Friends made in game. Friends invited to game. Come back (did they return to the app in the same session).
Exploring new metrics: find a way to gauge developer involvement with community. Player base sustainment statistics for developers. Genre leaders.
Also: explore ways to punish developers who abuse the incentivization system. It'd be easy to make players spend more time on a game by slowing down processes... that is unethical and should be punsihed.