Solid game play paired with Portal-quality writing makes this an unquestionable 5/5.
Suggestions: Either increase the costs of upgrades, or make more of them. I was completely upgraded for the last three normal levels, and they got fairly boring (except for the AI in between).
Scoring should emphasize solving the case as quickly as possible, and there should be something to make me want to play more than a few games. Add in some persistence from game to game and this is a 5-star.
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