Very fun little game! Played it for hours until I won (staying up WAY too late in the process), and it was fun for most of it. Sometimes frustrating, but never boring or tedious. I didn't realize for a long time how powerful the "Trade" upgrade was; I assumed the trade was only once, but it will repeat until you're out of moves! Absolutely necessary in the later levels when the scanners are unavoidable and can eat down your entire time in less than a second.
Big issue I noticed is that "Viral Chains" upgrade doesn't actually do anything (says it's supposed to slow down the scanners upon detection, but doesn't).
Some other issues I had was that there is no in-game pause button or way to get to the settings after starting a game; you have to click outside the window or otherwise switch windows to get to the pause menu. So if you want to change your colors or restart because you've messed up your run early on, you either have to spend the time to purposely run out of money, or close and restart the game.
My other issue was probably more a me thing, but I found the buttons to be opposite what was intuitive. Since you'd usually be using the search wave first and the infect second, and it automatically sets you to search mode first at the beginning of each floor, I had a lot of trouble remembering that 1 was actually for infect and 2 was for search (especially when later in the game and after I had the "invisible node infection" upgrade I would start a floor by taking a lot of "shots in the dark" with the infection. Since it takes a moment to register the switch, I would sometimes click too soon before the 1 button could register and search by mistake, and then assume I hit the wrong button since I was already constantly second-guessing myself about it, and ended up just keeping it on search and accidentally burning through many many moves trying and failing to infect). Some sort of indication of which mode you're on could be nice (especially for people using the Tab key). Edit: I may be stupid there literally is at the bottom
Lastly, some of the rangen with the upgrades and when the different difficulty increases (namely the second scanner) would show up made some runs feel a little unfair, since just being unlucky could seriously mess up an otherwise good run. Though I know it's hard to balance consistency and variation, so this is definitely another minor one.
This is not an issue so much as an idea, and of course there is no pressure at all for you to use it (especially if you're not updating the game), but an idea for another upgrade is one that speeds up the pulse around the nodes, so they don't linger so long that the scanners have the chance to hit the entire screen before they fade in the later floors.
Sorry this probably sounds like I'm just complaining, but I really did enjoy the game! Like I said, although sometimes frustrating, it was never tedious, which is very impressive with a game where you have to restart from the beginning and replay the first few levels a lot. I also really appreciated that the tutorial doesn't repeat at the start of every run and instead has a separate option to replay it from the menu. The graphics were both fitting to the premise and effective in gameplay, and I liked being able to customize the colors.