Your code is actually good. The project can be used as a skeleton for other Doom-like Java-based games. You can even create Wolfenstein-like levels using Tiled here. That's really impressive! Most importantly, it works unlike many other open-source FPS games published on GitHub. The hardest part was fixing blinking textures. Thankfully, my friend told me about sprite atlas edge padding.
If you want, we can have a group call and play a couple of matches. I'm actually struggling getting enough people to load-test the server.