Remix: Fever Trip

Build a small, playable browser game inspired by "Fever Trip" (Action, Adventure, Shooter).
Concept: An agent is sent to investigate a strange occurance but soon realises he's in the midst of a war with aliens, and he must also fight with his inner demons (quite literally) before he loses his sanity (fps game).
Tone/hook (from the game's own page): Fever Trip — a browser-based tactical FPS. Fight through planes, offices, deserts and forests. No install needed.
Tech: use Three.js; keep it to a single page that loads instantly with no login or install.
Controls (as seen on the original's screen): WASD to move, mouse to aim or look, click to shoot/attack, Shift to sprint/dash. Show them on a short how-to-play screen.
Players: single-player.
Core loop: include a visible score, a timer or round clock, levels, stages or waves that ramp up, progress saved in localStorage.
Steps: 1) get the core mechanic playable with placeholder shapes, 2) add win/lose conditions and restart, 3) polish feel, visuals and sound, 4) add your own twist (setting, character or one new rule).
Make it your own: don't copy the original's name, art, text or code.