There was one thing I didn't factor into my expectations for this game - mental fatigue. Now that the levels are starting to become more intense, it's a real problem. The enemies have started coming really fast and there are so many of them that my mistakes are really adding up. This means that I have to devote the entirety of my attention to the game lest I miss a click and take an unnecessary hit.
It feels really good when you slide into the right level of focus - your furious mouse-clicks send your little stick figure flying across the screen and then suddenly you find yourself pressed between two oncoming enemies, but a quick double-tap of the mouse buttons takes them both out, and it feels like your whole mind is being channeled through your fingers.
But if your focus is stuck at one level below the threshold, then the whole thing is a disaster. You miss clicks and get pummeled and the game gently chastises you for not paying close enough attention.
I feel like the best way to play One Finger Death Punch is in one-hour bursts, no more and no less. You need some time to get warmed up and find the proper mental state and then you need to quit before you burn out.
Yet within the framework of one-hour bursts, I think you could probably play this game indefinitely. The skill ceiling is super-high, the animation is hilarious, and actually beating a difficult level is a total rush. My biggest fear for my personal playthrough is that I'm certain I will rapidly hit the physical limit of my reaction time far before I actually complete all the levels. I'm fairly optimistic that I'll get to at least Master level before then, but I have a feeling that the game is going to make me sweat for it.