Great game! I think the idea and execution are very solid. Polish is incredible too. Some design suggestions + 1 bug report:
- I just got a game that went on for very long, and for this type of game, I believe you should strive for short and sweet sessions where losing is just around the corner (or else it gets repetitive and the player loses the will to think strategically due to fatigue). Being turn-based, this is especially true.
- I'm convinced ramping up the difficulty quicker will make the experience more enjoyable, increasing the feeling that every decision counts. This can be done is several ways (increasing 'bad events' spawn over time, ramping up speed of VOID quicker, adding more 'bad events', etc). To illustrate my point: the most fun I have in the game is when the VOID is near and I have to think carefully where to go next. When the VOID is far away and you are just chasing points, the game is the least enjoyable, in my experience.
- If you feel increasing difficulty might reduce enjoyment for more casual players, might be worth adding a "hardcore" game mode or similar.
- EDIT: Forgot to add the request to save game - perhaps this would be less important if games were shorter (see points above).
- When switching upgrades, if you hover over the old ones (to be switched out), their text is bugged in several cases (but not always).
Finally, congratulations on making such a clever little game. Looking forward to updates in case you plan on supporting the game further. Cheers!