diff --git a/_bmad-output/implementation-artifacts/sprint-status.yaml b/_bmad-output/implementation-artifacts/sprint-status.yaml
index 2be6f43..31f06b1 100644
--- a/_bmad-output/implementation-artifacts/sprint-status.yaml
+++ b/_bmad-output/implementation-artifacts/sprint-status.yaml
@@ -47,9 +47,9 @@ development_status:
   1-1-project-scaffold-and-dev-environment: review
   1-2-game-logic-module: review
   1-3-game-board-and-tile-rendering: review
-  1-4-game-header-score-display-and-new-game-button: backlog
-  1-5-keyboard-input-and-interactive-gameplay: backlog
-  1-6-win-and-game-over-overlays: backlog
+  1-4-game-header-score-display-and-new-game-button: review
+  1-5-keyboard-input-and-interactive-gameplay: review
+  1-6-win-and-game-over-overlays: review
   epic-1-retrospective: optional
 
   # Epic 2: Save Progress & Keep Playing
diff --git a/src/App.svelte b/src/App.svelte
index 8c82ab6..507f130 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -1,7 +1,10 @@
 <script>
   import Grid from './components/Grid.svelte';
-  import { initGame } from './lib/game-logic.js';
+  import ScoreBoard from './components/ScoreBoard.svelte';
+  import GameMessage from './components/GameMessage.svelte';
+  import { initGame, move, isGameOver } from './lib/game-logic.js';
   import { GRID_SIZE } from './lib/constants.js';
+  import { getDirectionFromKey } from './lib/input-handler.js';
 
   let gameState = $state(initGame());
 
@@ -17,8 +20,56 @@
     }
     return result;
   });
+
+  let overlayType = $derived.by(() => {
+    if (gameState.won && !gameState.keepPlaying) return 'win';
+    if (isGameOver(gameState)) return 'gameover';
+    return null;
+  });
+
+  function handleNewGame() {
+    gameState = initGame();
+  }
+
+  function handleKeepGoing() {
+    gameState = { ...gameState, keepPlaying: true, won: true };
+  }
+
+  function handleKeydown(event) {
+    const direction = getDirectionFromKey(event.key);
+    if (!direction) return;
+    event.preventDefault();
+
+    if (overlayType === 'gameover') return;
+
+    const newState = move(gameState, direction);
+    if (newState !== gameState) {
+      gameState = newState;
+    }
+  }
 </script>
 
-<main class="max-w-[500px] mx-auto pt-10">
-  <Grid {tiles} />
+<svelte:window onkeydown={handleKeydown} />
+
+<main class="max-w-[500px] mx-auto px-2 pt-6" role="application">
+  <header>
+    <div class="flex items-center justify-between mb-2">
+      <h1 class="text-[80px] font-bold leading-none" style="color: #776e65;">2048</h1>
+      <ScoreBoard score={gameState.score} bestScore={0} />
+    </div>
+    <div class="flex items-center justify-between mb-4">
+      <p class="text-[18px]" style="color: #776e65;">Join the numbers and get to the <strong>2048 tile!</strong></p>
+      <button
+        class="font-bold text-[18px] rounded-[3px] px-4 py-2 min-h-[44px] min-w-[44px] cursor-pointer"
+        style="background: #8f7a66; color: #f9f6f2;"
+        onclick={handleNewGame}
+      >
+        New Game
+      </button>
+    </div>
+  </header>
+  <div class="relative">
+    <Grid {tiles} />
+    <GameMessage type={overlayType} onKeepGoing={handleKeepGoing} onNewGame={handleNewGame} />
+  </div>
 </main>
diff --git a/src/components/GameMessage.svelte b/src/components/GameMessage.svelte
new file mode 100644
index 0000000..9e37655
--- /dev/null
+++ b/src/components/GameMessage.svelte
@@ -0,0 +1,44 @@
+<script>
+  let { type = null, onKeepGoing = () => {}, onNewGame = () => {} } = $props();
+
+  let message = $derived(type === 'win' ? 'You win!' : 'Game over!');
+  let bgColor = $derived(type === 'win' ? 'rgba(237, 194, 46, 0.5)' : 'rgba(238, 228, 218, 0.73)');
+</script>
+
+{#if type}
+  <div
+    class="absolute inset-0 flex flex-col items-center justify-center z-10 rounded-[6px]"
+    style="background: {bgColor};"
+    role="alertdialog"
+    aria-modal="true"
+    aria-label={message}
+  >
+    <p class="text-[60px] font-bold mb-4" style="color: #776e65;">{message}</p>
+    {#if type === 'win'}
+      <div class="flex gap-2">
+        <button
+          class="font-bold text-[18px] rounded-[3px] px-5 py-3 min-h-[44px] cursor-pointer"
+          style="background: #8f7a66; color: #f9f6f2;"
+          onclick={onKeepGoing}
+        >
+          Keep going
+        </button>
+        <button
+          class="font-bold text-[18px] rounded-[3px] px-5 py-3 min-h-[44px] cursor-pointer"
+          style="background: #8f7a66; color: #f9f6f2;"
+          onclick={onNewGame}
+        >
+          New Game
+        </button>
+      </div>
+    {:else}
+      <button
+        class="font-bold text-[18px] rounded-[3px] px-5 py-3 min-h-[44px] cursor-pointer"
+        style="background: #8f7a66; color: #f9f6f2;"
+        onclick={onNewGame}
+      >
+        Try again
+      </button>
+    {/if}
+  </div>
+{/if}
diff --git a/src/components/ScoreBoard.svelte b/src/components/ScoreBoard.svelte
new file mode 100644
index 0000000..2d5e597
--- /dev/null
+++ b/src/components/ScoreBoard.svelte
@@ -0,0 +1,14 @@
+<script>
+  let { score = 0, bestScore = 0 } = $props();
+</script>
+
+<div class="flex gap-2">
+  <div class="flex flex-col items-center rounded-[3px] px-6 py-2 min-w-[80px]" style="background: #bbada0;">
+    <span class="uppercase text-[13px] font-bold" style="color: #eee4da;">Score</span>
+    <span class="text-[25px] font-bold" style="color: #f9f6f2;" aria-live="polite">{score}</span>
+  </div>
+  <div class="flex flex-col items-center rounded-[3px] px-6 py-2 min-w-[80px]" style="background: #bbada0;">
+    <span class="uppercase text-[13px] font-bold" style="color: #eee4da;">Best</span>
+    <span class="text-[25px] font-bold" style="color: #f9f6f2;">{bestScore}</span>
+  </div>
+</div>
diff --git a/src/lib/input-handler.js b/src/lib/input-handler.js
new file mode 100644
index 0000000..a98726a
--- /dev/null
+++ b/src/lib/input-handler.js
@@ -0,0 +1,12 @@
+import { DIRECTIONS } from './constants.js';
+
+const KEY_MAP = {
+  ArrowUp: DIRECTIONS.UP,
+  ArrowDown: DIRECTIONS.DOWN,
+  ArrowLeft: DIRECTIONS.LEFT,
+  ArrowRight: DIRECTIONS.RIGHT,
+};
+
+export function getDirectionFromKey(key) {
+  return KEY_MAP[key] || null;
+}