Pretty fun! I was surprised, because of how active this incremental game is, to put it down overnight and find my prestige points had gone up by roughly 40 playthroughs the next morning.
I got as far as the second boss fight - by that point my refresh rate was something like one frame a second - and after dying to it the game decided not to respawn me anymore. I'd say it froze, but I can still access the upgrade menus.
I'm assuming difficulties unlock with play? I wasn't able to select anything but Easy Mode from the start menu.
There's a point about 20 waves in where the game reliably dumps something like 20grand in points on the player, and if they don't spend it on upgrades within a few seconds they're toast. I'm not sure if that was as intended or if that wave has some scaling issues?