Superb stealth implementation and hilarious AI quips keep this lengthy game entertaining, but beware the Grey lady.
If you move out of the shadows a guard will think he saw something, so he moves to the spot, if you have moved off or into the darkness he will assume it was nothing and continues on his way. At this point since he is unaware of your presence a single arrow to the back will dispose of him. A lowly citizen might see this body; he gets frightened and runs off to the nearest guard for help. This guard comes back and searches the area with sword in hand, ready for a fight. Now a single arrow won't work, rather it serves to annoy and partially damage the guard, as the game wants to reward stealth rather than action. After some time the guard will be mystified and go about his merry way.
The fuzzy detection system is great, there never appears to be an imaginary line of detection, its very much based on how long you are in the light, how far away you are and how much noise you make but you can never be sure and need to listen to enemies responses and most of the time they will be comical. The AI can be a great laugh when they are after taffers. There will be times when you get seen, at which point you can dart away, guards usually tire of running and you can hide in the shadows again. Otherwise you can use you bag of tricks including a flash bang type device, gas grenades, mines and more to keep them off your back, there are some dynamic moments associated with these devices like setting up traps and gassing multiple enemies as their paths cross.
The game missions take you across various parts of the city, the city is open to you but patrolled by guards, you can steal from places many times. You can pick up arrows that regularly return to the cityscape in the same spots. The loot you acquire during missions or free roam can be sold to fences and then you can buy (but not sell) items like arrows and health vials. Water arrows can be used to douse fires keeping you in the dark, you'll be using these quite a bit. The game takes you through a story and opens up doorways to levels to do what thieves do best.
The story unfolds via some inconsistent hand drawn and some rather poor 3D cut scenes but they get the message across sufficiently. The maps aren't particularly large; missions are usually made of two or three maps. The game quits to desktop and restarts every level load, which is quite irritating. Also sometimes your animation will get stuck in a half jump move, making Garrett pretty useless again forcing a reload. Despite these and other minor problems the nicely varied missions and superb stealth detection system make it well worth looking at.