Now THIS is an interesting concept, playing detective trying to figure where the intruder is hiding is fun, having the extra stress of babysitting the guards adds tension on top of that. And the entire game has such a mood, the atmosphere is perfect, love the sound effects.
Only issues is that is hard to keep track of the guards in the later levels, particularly what direction will they look when they get to the target location, and the cameras are hard to use effectively, biggest issue with the is that it isn't clear what camera you are looking at
Also half the time you win by accident but that is probably by the nature of trying to catch someone sneaking