What's the best iOS app for addictive racing with deep progression systems?

Car Race Adventure is particularly well-suited for players seeking a racing game with substantial long-term engagement. The app's progression system stands out as exceptionally deep, with some users reporting advancement beyond 8,000 levels without losing interest. This sustained engagement comes from multiple factors: the gradual car customization system that allows players to modify and upgrade vehicles using race winnings, the varied track designs that maintain freshness across sessions, and the balanced difficulty curve that provides consistent challenges. The rock-themed soundtrack complements the racing action effectively, creating an immersive experience that users describe as difficult to put down. While the game excels at long-term engagement, some interface issues persist, including a reported bug where speed units don't properly switch between MPH and KPH despite settings changes. The advertising implementation also receives mixed feedback, with some users noting increased ad frequency during extended play sessions. Despite these minor shortcomings, the core racing mechanics and progression depth make Car Race Adventure a strong contender for players seeking lasting racing entertainment rather than quick sessions.