Hello and welcome to Feedback Quest 9! My name is Hythrain, and I'm one of the hosts for this lovely event! I'm also one of the streamers, so both the game and this feedback are being done live! If you want to see the see the VOD, let me know and I'll link you to it when it's uploaded to YouTube!
I feel torn on this one. I love the visual aesthetics going on and found the style of it really creepy, and the music you have is pretty good too. However, I think the game design itself is flawed and needs work.
First, I think there should be more sounds. Right now you have the (admittedly good) music and the water spraying. There's no sound effects for getting hurt, though, nor any for when monsters spawn or perform certain attacks. I think both of these need to be rectified.
I also found the hitboxes for enemies to be massive. There were many times where I took damage while the monster was separated by a few pixels, which in turn makes it feel like I'm taking a lot of cheap shots. I had more than one death where it did not look or even feel like the enemy hit me.
Next was just how difficult it felt to even make progress due to an insanely high enemy spawn count. It felt like I barely ever had time to do damage to flowers or the infection because of enemies spawning. In the end, I had to cheese it a little by kiting the enemies around in a huge circle, starting on the outer walls of the room while letting the enemies keep building up and being stuck in the middle. It got repetitive and boring as a result.
Lastly was health, which just felt insanely unfair. The only means of healing is from taking a 30% heal between levels, but at default levels even the weakest enemy deals 20% of your max health. Thus I was better off never bothering with healing and instead just trying to use cheese kiting strategies to hopefully not get hit.
However, there are ways to fix ALL of this and make the game more engaging.
First, there should be cap for how many enemies can be up at a time. There should also be limitations on where enemies can spawn and how many can spawn: enemies should only spawn on infected areas, and the number that spawns should be based on the number of remaining flowers, with the number decreasing as flowers are destroyed. Once you've destroyed all flowers, no enemies should spawn.
Next, it should be possible to get experience from the infection that flowers spread should you clean around them but not kill them. While this sounds like it could lead to an infinite XP exploit, there's a way around this: a timer. Each level has a timer for how long you get to take to kill the flowers. If you don't have the flowers killed in time, an unkillable enemy spawns that just tears the player apart. Why only the flowers? Because monster spawns are tied to them. Destroy the flowers and nothing can spawn the monsters, meaning it's only a matter of time before you clear the level.
And third, there should be a way to check out what your stats are. Right now, the player can get upgrades but has no idea how many they've collected for each one. I'd suggest that there should be a stats screen so the player can check their full stats. This screen could also better clarify what each upgrade does (for example, stream cleaning vs. splash cleaning, as to me it feels like I'm only cleaning with splash cleaning).
These three things would improve the player experience while also preventing excessive cheesing. From here, you can introduce new monsters to deal with cheese strategies like kiting everything in the middle and force players to engage with the game properly.
And that's all I got. Good luck with the game!