The most special thing about Hill Climb Racing is its addictive and simple yet challenging gameplay. The game combines physics-based mechanics with a variety of vehicles and terrains, requiring players to carefully balance speed and control to avoid flipping over. Each level presents unique obstacles and challenges, keeping the gameplay fresh and engaging. Additionally, players can upgrade their vehicles and unlock new ones, adding a layer of strategy and progression to the game. The charming graphics and whimsical sound effects also contribute to its appeal, making it a favorite among casual gamers.