Earn the "Predatory Drive" achievement for taking 15 hours or longer to finish the game.
Stealth games are a different breed. A huge portion of the genre's draw is to take your time, soak in the atmosphere, and become an electronic voyeur. I vividly recall that tingly feeling of trespassing that I felt on my first exposure to Thief 2. While more modern installments in the genre try to be more flexible and slip in some action, the upcoming Thief reboot aims to keep things more or less traditional. Recently, gaming site Xbox Achievement recently got a hold of Thief's 'cheevo list, revealing that the game rewards players for taking the time to slow down and smell the shadows.
The "Predatory Drive" achievement earns you 30 Gamerscore for finishing the game in over 15 hours. It might be a nice encouragement for some players, as it can be tempting to take the easy way out in these games.
More recently, Dishonored withheld the good ending unless players behaved themselves and played non-violently, something our own Robert Rath did a great job exploring. Even so, it was still possible to skip all the side missions and miss out on the wonderful exploration, resulting in a remarkably abbreviated game. It's easy to spoil a good stealth game with a lack of patience. Regardless, we'll see how Thief turns out when it launches on February 25th for the PC and current and last-gen consoles.
Source: Xbox Achievements