In brief: A team of dedicated fans worked for seven years to bring an all-new experience to Thief, the game that popularized the stealth genre back in the late 90s. The Black Parade is much more than just a "simple" expansion as it also makes use of modern AI to boost difficulty.
When it was released in 1998, Thief: The Dark Project challenged the then-popular mechanics of the first-person shooter (FPS) genre with innovative, slower "first-person sneaker" gameplay. Players took control of a master thief trained by a secret society, completing a set of objectives in each mission while trying to avoid being detected as much as possible.
Thief combined unscripted levels and complex AI algorithms to deliver one of the earliest emergent gameplay experiences on PC. Developer Looking Glass published an expanded edition of the original game in 1999 (Thief Gold) with modified missions and a few new levels.
Thief: The Black Parade is an all-new, fan-made campaign by Feuillade Industries that adds a remarkable amount of new content to the 25-year-old series. The expansion includes 10 additional missions featuring a brand-new protagonist and a dark story of "crime and conspiracies."
The Black Parade also introduces four new tools sold through the underground market, numerous tweaks to the original AI that make the game a bit more challenging yet still fair, and a new "banter" system for funny interactions between AIs. The expansion features 28 voiced characters with roughly 1,800 new lines of dialogue, along with 30 minutes of hand-drawn cutscenes and full English subtitles.
Additionally, The Black Parade introduces a new AI-based motion system designed to make the denizens of The City – the fantasy metropolis the original game is set in – look more "alive." Last but not least, the expansion brings some changes to the classic Thief gameplay, offering a novel experience even for the most seasoned Thief players.
The Black Parade can be downloaded for free from the TTLG (Through the Looking Glass) forums. The package requires the NewDark update, a fan-developed patch designed to enhance the Thief experience on modern PCs.