I ended up taking a risk on "Everyday Genius: Square Logic" hoping it would fill my desire for a Killer Sudoku game (it's not quite the same, but it is a varition which is quite enjoyable) and I have to say I'm extremely impressed by how many puzzles are available, and the ability to alter how much help it provides (auto-elimination, showing of possible solutions, and highlighting of errors immediately or afterwards). I do have some small qualms with it, primarily that numbers within cages are able to be reused (ie a possible solution to 5 is 2, 1, 2), the difficulty of the first world at least is far too low for anybody with prior experience with the type of puzzles (but I imagine that they're a good training excercise if you don't) given that it only uses one to four, and following that, one to five (I assume it progresses further, with each world adding an extra digit, or at least I hope so), and I don't like some of the alterations (some puzzles not showing the cage boundaries. Overall, I would very much recommend it to anybody with an interest in these type of logical puzzles, but I would stress the need that, if you've prior experience with any variation of Sudoku, turning off the help (which can make it almost as if it's on autopilot), and rushing through the first few worlds to get to the more challenging puzzles (which admittedly you'll breeze through if you've prior experience anyway so this doesn't take too long), is going to be required. This isn't a knock against it however, as there are more than enough puzzles to suit those with experience and those without experience alike. Thank you very much for this recommendation Toma!