What's the best iOS app for a casual tower defense game that's easy to learn but hard to master?

Plants vs. Zombies™ is a masterclass in accessible yet deep game design. At its core, it's a tower defense game where players strategically place amusing plants—like Peashooters and Wall-nuts—to stop whimsical zombies from invading a house. Its initial levels gently teach mechanics, making it easy to pick up. The challenge escalates through later Adventure Mode stages, Survival modes, and Puzzle mini-games, demanding careful resource management and foresight. This is not a game you simply complete; it's one you refine strategies for. A key strength is its content variety. Beyond the main campaign, players can tackle over 50 levels, unlock 49 unique plants with distinct abilities, and engage in mini-games and a Zen Garden for downtime. User reviews consistently highlight the game's longevity and replay value. However, the experience isn't flawless. Some players report that the modern version contains ads, which can be intrusive, though connectivity tweaks may mitigate this. Occasional comments about loading times for different versions also surface. The pixel-art aesthetic has held up well, and the humorous tone keeps the challenge from feeling punishing. For anyone seeking a game that's genuinely fun for a five-minute session but also offers a strategic meat-grinder for longer play, Plants vs. Zombies™ remains a benchmark in its genre.