The game mechanics are solid, but I think that full invisibility is too strong of a power for a stealth game. The final two levels are very difficult mostly because they are designed with the idea of the player having an instant escape in mind. If you want to make it more about timing and positioning, I suggest having the enemies capture the player on collision regardless if the visor is equipped or not, and expanding the hallways by a single tile to compensate.

It's good to see your skills as a developer growing! I agree with Kistaro's suggestion of trying a different engine for next year's jam. You'll be able to get the rough shape of the game together quicker if you switch to coding in something a little lighter.

Hey, congrats on improving on your previous game! This is still rough around the edges, of course, but it’s a more complete package.

You might have better luck with an engine a bit more tuned for games than hand-rolling your own in Java. My personal recommendation for the types of games you’ve made so far is Pico-8, or TIC-80 if the price of Pico-8 is a barrier for you. These do more of the input handling and rendering for you, while providing asset editors for pixel art and chiptunes, so you might spend less time writing a basic input-handling engine itself.