Played this back when it first came out, but recently revisited it and god damn if it isn't still pretty great! Needs more opposition, though; I notice commenters mentioning a "ticking clock" element, like maybe the guards call in backup if you trap them in a room, but personally I think there needs to be a rival hacker; somebody to directly oppose Casey, an antagonistic force going after the player character themselves. It'd give the whole thing more tension and more personal stakes, having to fight an enemy who can challenge Casey on their level. Maybe they can "counter-hack" the programs the player already has control over. This would have the added benefit of preventing the "soft-locking" situation that one of the commenters below mentioned, where if you have all your slots full of one color key without anything to hack, you're basically screwed.