Okay so it looks like you weren't kidding when you called it endless. Games like this need a way to ramp up the difficulty to prevent players from going on forever. I stopped at level 103 with a score of 2267 because I could see it wasn't getting any more difficult. In PACTIME, I prevent players from playing forever by steadily incrementing across 21 levels of difficulty, and level 21 is so difficult that I don't imagine anyone can last very long. I'm not sure what variables you can change to increase the difficulty over time, but for example the thermometer could refill more slowly making you need better shots to get more hits.