I frequently update a small thing on an online game, and then go to test it. Sometimes I get sucked into the game as I am testing it, and wind up playing and getting caught in the flow of it, which is a very good sign. Other times when I go to test, I feel like, "Ugh, this is tedious," and that lets me know something needs to change in the game.
So even though, sometimes I think the game, if I reduced it to it's dry mechanics, and so forth, should by no rights be that good, if I get caught up by it and interested, then my experience is telling me that it is working well. Because there is something beyond the dry mechanics of a game, and analyzed parts, something that relates to the totality of your experience as a human being during the game. Some parts of that are hard to define, because human beings are complicated. But if you know that people bring their whole self and life to everything, then you can evaluate your game based on that type of totality, rather than on a reductionist approach to it, because the reductionist approach invariably misses those ephemeral, hard-to-define parts.