Hey, this is excellent! I had a great time, and didn't find it too frustrating (a smidge frustrating, but an acceptable smidge). I have some suggestions though:
The biggest issue I had was the blind jumps. It's a bit annoying flinging myself into walls that I had no way of knowing were there, or dropping onto hazards that were off screen. Check my playthrough video for examples, I point it out basically every time. You could benefit a lot from a more dynamic camera, or maybe just zooming out aggressively. You would need to pair this with my second suggestion for it to not break the controls though...
The controls are... well they're fine. Fun even. But a bit... eh... uncomfortable. I wouldn't want to play this for hours, it'd hurt my wrists. I think you could improve it a lot by breaking the 1:1 relationship with the mouse position and the tongue position. Let me use my entire screen, and not just the tiny portion of it near the character. This is even more exacerbated if you're not playing in fullscreen, pay attention to that in your playtest data, I'd suspect anyone who doesn't fullscreen will struggle more. Heck, you could make it like a fps where you "lock" the cursor to the screen and just write your own tongue control logic, this would let you add a sensitivity slider and everything too. Might even be worth having a "precise movement" button you can hold down to reduce the sensitivity, idk, something to try.
However, I think the biggest missed opportunity is a very simple one. You should make this a mobile game. Seriously. Godot has automatic touch to mouse conversion. You're like 2 simple changes away from supporting mobile, and that would just feel so nice, it'd probably solve the uncomfortable controls for a lot of people instantly; touch screens are far more intuitive. I tried to load the game on my phone, there are some minor issues you'd have to sort out: 1 - the tongue lags like a frame behind the cursor, so when you touch the screen you grab the wall where the tongue was and not where your finger is. This is very annoying and makes it way harder to play than intended, you'll see what I mean immediately if you try to load the game on your phone. 2 - phones don't have keys, so you'd need an on screen restart and pause button. Oh and I guess 3 - flag it for mobile support in itch so it doesn't give scary warnings about incompatibility.
I have my gameplay recorded for reference. Keep in mind I'm not a content creator, these are just the ramblings of a dev.
Anyways that's all I got for now. I followed your itch page, looking forward to future updates... if you have a discord or something, I'd consider joining.Also would love if you checked out my submitted game, but there's no obligation, I checked your game out simply because I wanted to! But, it's in a similar genre so I figured maybe you'd have constructive thoughts, or possibly (hopefully) even like it.