We can't assess the quality of gameplay ourselves of course (since the model wasn't released), but one author said "It's playable, the videos on our project page are actual game play." (https://x.com/shlomifruchter/status/1828850796840268009) and the video on top of https://gamengen.github.io/ starts out with "these are real-time recordings of people playing the game". Based on those claims, it seems likely that they did get a playable system in front of humans by the end of the project (though perhaps not by the time the draft was uploaded to arXiv).