Cancelled sequelWhen you finish the game, the bad guy escapes and after the credits it says the series will conclude with part 3. Which was never made. You could see a box with Manhunter: London somewhere in the game.
EngineThe game was actually Sierra's last to use the AGI game engine that they started way back with King's Quest. A lot of people don't even notice the fact that the game engine is the same, since the interface was so different.
Information also contributed by Jason "Paco" Artman, Olivier Masse and woods01