Nothing beats the delightful uplifting feeling when your test player genuinely enjoys playing your game. It's also eye opening to see how each test player brings their entire life history into the test run. The way logic works in slightly similar, yet completely different way inside everyone's head. I haven't yet met a single test player who had played my game exactly the same way. There is still a lot of work to be done for game to be a working, polished whole, but every test run, every development burst gets me closer to finalized version, the ominous game 1.0.