Cool idea! As some others have mentioned, there were a few bugs (like the recoil problem) that made it less fun. In addition, I think it might be interesting to give the player a warning (maybe a subtle countdown effect) when the gun style is about the change.

It might also be fun to go all-in on the franticness: make the weapons change faster, make the zombies faster, make the player faster, etc. And some obstacles would help with positioning.

I like the idea. However, when the weapon mode switches, that should be a lot more obvious! As of now, "Backwards" into "Knockback" is a death sentence. Maybe display the new mode above the hero and/or crosshair? Pause or slow down the game briefly after the mode switched? Display a timer that shows how long the current mode will still last, so you can plan around that? I also found myself skipping "Spin" all the time: given that you move faster when not shooting, there really is no point in using it. The chances of you hitting anything like this are close to non-existent anyways and as enemies can take quite a bit of bullets, even hitting them oftentimes wouldn't change anything! From a game design standpoint I liked the "no aim" mode most, as it usually forces you to navigate into awkwardly risky spots if you want to keep hitting enemies while it's active. Lastly I would have liked a way to refill hearts to make up for early mistakes. Maybe reward the player with +1 heart (but maximum 5) after each wave of enemies?

Duuude! That was fun! Only made it to wave 4 though, gun chose a really bad moment to go "No aim" mode..

The game is very interesting, although could use a ton of cleaning up. Two of the biggest bugs I noticed were that the recoil on the "knockback" mode of the gun only works in one direction, and that the zombie noises are for some reason only in the left ear. I think this could turn into something, but for that to happen it needs a lot of work.