This page is for the original game. For the 2014 reboot, see Thief (2014).
TFix updates the game with NewDark for modern systems. Also contains mission fixes and optional texture mods. The GOG release has an out-of-date, stripped-down version of this patch.
The Enhancement Pack 2.0 is an updated version of the original Enhancement Pack (which is included in TFix and is much less comprehensive). This contains higher quality reproductions of original textures and objects. Also works with Thief II: The Metal Age.
The Necro Project pack is very similar to the Enhancement Pack 2, but focuses on giving the game a slightly darker, noir look. Somewhere between the EP2 and HD Mod in lore-accuracy. Also works with Thief II: The Metal Age.
The Thief Gold HD Texture Mod adds new textures, effects and enemy skins to all original missions. Significantly alters the game's graphical style (far more than the two packs above). Only compatible with Thief Gold. Includes a tool to configure advanced graphics settings (Anti-Aliasing, Bloom, etc.). An FAQ with installation steps is available.
Install NewDark via TFix.
If you still can't change gamma:
GoldToDark is a patch that will convert Thief Gold into the original Thief: The Dark Project. This must be used on a clean installation of Thief Gold. TFix can be installed thereafter and should correctly detect that you are using The Dark Project instead of Thief Gold.