TL;dr: 4 stars because it's a fun enough game, but it's ultimately held back by balance and design issues.

Short semi-idle game (~4 hours to 100%) with an unusual gameplay loop that takes a bit of wrapping your head around. You are a square that occasionally auto-deals damage, and when damage procs you attack any other geometric shapes on screen which overlap you. Kill those shapes and they drop one of five resource types to upgrade yourself with. Fail to kill them and they deal damage to your HP bar. Survive long enough and a giant boss appears, to drop a rare resource and let you advance to the next prestige level (scaling enemies and drops).

Generally fun, with a large upgrade tree, but there are some deeply odd design decisions -- for instance, killing the boss instantly ends the level but does not pick up any uncollected resources, forcing you to scramble around the screen to scoop up currency whenever the boss starts getting low on health, which can be lethal if your autoattack blasts a bunch of mobs as you go. Your item pickup range caps fairly small and auto-pickup costs scale absurdly high (the last level, taking me to 80% efficiency, was literally the final upgrade I bought in the entire tree), so toward endgame you're basically just swirling your mouse frantically around the map to collect the currency from the things that your minions and chain lightning attacks remotely kill.

It also feels like the dev ran out of content at the end. There's basically no new content after Zone ~12, but the final endgame upgrade (the lab) doesn't unlock until zone 17 or so and the single thing you can do in the lab is so expensive it requires grinding to the final zone (25) and replaying it a few times. The Lab was honestly a mistake; the game should have just ended when it ran out of ideas rather than doubling the grind time just to see the end.

Late-game scaling is also weird. At some point you have enough vampirism on your attacks that your HP bar simply stops dropping. The only meaningful late-game wall is whether you hit-but-don't-kill enough enemies to one-shot you, at which point the level ends with no warning. Then you get a late upgrade which gives you permanent max HP boosts with every killed enemy, and another which scales your damage and armor to your max HP; at that point you're invinicible but still have to chase resource drops frantically around the screen. Also, the "Milestones" aren't calibrated to the content length -- I finished the game with three still incomplete despite the entire upgrade tree being long since finished.

It's worth playing on the strength of the early to mid-game design, but given that it's a paid game, probably pick it up on sale/in a bundle, or wait to see if an update smooths the experience out.