A major departure from the first two games in the series, Thief: Deadly Shadows was developed by Ion Storm rather than Looking Glass Studios (albeit with many of the same people). The game was powered by the Unreal-based Deus Ex: Invisible War engine. Unlike the original two titles, the third Thief game was developed simultaneously for Windows and the Xbox.
Because of all these factors, Thief: Deadly Shadows (Ion Storm decided not to name the game Thief III for fear that it would alienate console gamers who had never played the previous two titles) was different (and vastly updated) from the first two games in the series in both appearance and gameplay.
One of the game's major new features was the ability to explore the City. While previous games sent Garrett straight from mission to mission, Thief: Deadly Shadows allows him to walk the City streets between missions where he can steal from passersby, spy on the townspeople's daily lives, and search for sidequests in addition to major story missions. Unlike sandbox games such as Grand Theft Auto III, the city is not one large continuous map, but rather several small neighborhood maps connected by load zones (similar to Postal²). The game also introduced an ability to switch between first and third person views, and to flatten against walls.