Maybe you need not pre-installed games and rather something like Gamesome frontend - launcher with selective game news, recommendations, filters, ratings, wise notifications, collecting feedback etc., with games downloading from Google Play, Humble Bundle Store, Amazon AppStore. Similar to TegraZone, Archos GameZone, Samsung S Console, PhoneJoy Gamepad App.
I think you need to organize a poll of what kind of Android games consumers and users of GPD devices playing most the time (apart from emulators, of course).
Something like an email asking kindly for following information:
Age Group (under 13, 14-19, 20-30, for example)
Name Top 5 of your favourite Android games
That could give you a understanding what companies producing the games your auditory plays the most, and about preferable genres. Once you will have such information, you can define potential partners among game developers/publishers. It also will help you improve your Game Center with Age/Gender/Country game recommendations.
And then we could give you an initial recommendations of good games for each mentioned genre.
You could use a feedback from the Game Centre to improve devices' compatibility by adressing problems if specific games to their authors. For example, Dot Emu and SNK Playmore games mostly unplayable on GPD G5A for now - they are crashing right after launch. You could collect users' reports and point them out to the game developers. I wrote to SNK once about their KoF ports, but my letter was ignored. Maybe your wouldn't be? It will also gain you some credibility among both consumers and game developers.
You can also create a better alternative to Happy Chick, where user will have an organised, intuitive and and timely updated base of Android emulators with installation of them from Google Play and authors' websites. And no pirated stuff, of course!