I would say this game is a 4/5, quite good for what it is.
The main pain point is the bossfight, although there are some mechanical issues throughout the game. I'll try to describe them since it seems no one else is (despite the developer asking).
General gameplay issues:
- It is very hard to tell when your boost is done charging, as well as how close it is to being done. The first issue can be solved by adding a halo or some other indicator when the boost is ready. But for the second, you might want to add a secondary bar in the side panel that repeats or replaces the boost charge gauge.
- Sometimes it can be hard to tell where your boost will put you. A ghost where you'd end up could solve this issue
- The upgrades seem pretty uneven in how useful they are, but maybe that's to be expected
Boss issues
- The boss is likely[1] too much of a difficulty jump, leaving a long-ish time where everything before the boss is easy but everything after hard
- Because the boss is so hard, it becomes almost pointless to continue into it until you're maxed out on upgrades. You won't beat the boss and you'll likely collect very few resources before you die.
- The boss's tail. I like that if feels tron-like, although the new mechanic came a little out of left field for a boss that's otherwise a bigger version of the other bad guys. However, frequently what will happen is I will try to boost behind the boss to stun, only to realize I was a milisecond too late, and the tail has popped into existance and insta-killed me. I would suggest either delaying when the tail becomes deadly, reduce the hurtbox on it, or have it so the stun also destroys an unconnected tail.
- The hit/hurtboxes in general should probably be reduced. If I boost near the boss in a safe spot and then he swivels and the tip of his nose touches one of my corners, that's insta-death. This is one of those times you should probably cheat for your player to make the game feel better.
- You might consider making infinitely repurchaseable upgrades after all the other upgrades are purchased, to keep the feeling of progression during the final stage, instead of it feeling like just slamming your head against the wall over and over. Alternatively, if other changes make the bossfight more managable, perhaps make a final upgrade that lets you skip the upgrade page (since it's now pointless--no more upgrades available)
Possible improvements
- The two most fun parts of the game are the collection/upgrade loop, and boosting through enemies. The former falls off later in the game as collecting becomes more of a slog and there are fewer killer upgrades left. To make the later part of the game better you might consider adding extra boost gauges as an upgrade, so people can have more fun blasting through their enemies. It might require a bit of a difficulty rebalance, though
- As a webgame, this game has the perfect amount of content, but if it's going on steam where people pay for it, it will probably need more bosses, enemies, and upgrades. I might suggest an enemy that has some version of the boss's tron tail, to get players used to that mechanic
- Also, the name is not great.
I made an account to post this feedback, so I hope it's helpful.
[1] Different games target different difficulty curves so it's hard for me to say for sure what a difficulty curve "should" be. Some players want animal crossing and some want dark souls. However, a sharp spike in difficulty is a sign to me of game needing better balance.