Pretty much full marks from me for this; this is impeccably implemented, with care taken over small details (such as the wipe transitions) which make it feel like a complete game rather than an exploration of a concept. Nice work. The graphics are clean and clear, the "spy/safecracker" theme is well expressed, and the world maps are cool. If I had a quibble, it's with the nature of the game itself rather than its implementation: once you realise the binary search technique exists (start each game with 55555) it becomes almost completely mechanical to play, which is a shame for such a nice game. (This is probably why Mastermind, which is also vulnerable to a similar sort of strategy but one which is a lot more mathematical and a lot less obvious, has been enduringly popular, and would probably map onto this game's UI quite well.)