SudoKoi Sudoku Killer is a fantastic Sudoku game for iPhone users. With up to five difficulty ratings and the ability to play up to nine Sudokus simultaneously, this game offers a variety of challenges for Sudoku enthusiasts. The game allows you to enter notes and keep track of candidates, and also provides features like highlighting numbers, error checking, and undoing actions.

What sets SudoKoi apart from other Sudoku games is its intuitive design. The app provides assistance where needed, such as highlighting neighboring cells and showing indicators for completed boxes. However, it never takes away the challenge of solving the Sudoku yourself. The controls are well-designed and make playing Sudoku on your iPhone a breeze.

Visually, SudoKoi is elegant and unobtrusive. The design is well-crafted and looks great on all devices. The game is both aesthetic and understandable, making it a pleasure to solve Sudokus with SudoKoi.

In addition to its gameplay features, SudoKoi offers statistics, a strategy guide, sharing options, assisted candidates, advanced controls, and scanning capabilities. While the game is free and comes with a selected number of Sudokus and Killer Sudokus, you can upgrade to SudoKoi+ for access to thousands of handcrafted Sudokus and Killer Sudokus.

Overall, SudoKoi Sudoku Killer is a simple, elegant, and enjoyable Sudoku game for iPhone users. Whether you're a beginner or an experienced Sudoku player, this game provides a great experience with its intuitive design and range of features.