Gameplay is similar to what you'd find in the Thief games. In other words, in each mission you have to complete a series of objectives that range from killing a specific person to stealing an artifact, with some simple exploration mixed in. The thing is, your protagonist is not a warrior, but a thief.
That means that instead of choosing between a wide variety of weapons to finish of your enemies, you'll have to get by with some different pieces of equipment designed to make your life a lot easier. They include smoke bombs to help you disappear, water arrows to put out torches, moss arrows to break your fall... and the ever-useful billy club to knock out enemies.
The Dark Mod comes with an in-game client that allows you to download dozens of different missions, some of which were created by users. Before starting each mission, just like in the Thief games, you'll need to buy the items that you want to take with you.
Graphically, The Dark Mod is spectacular. The game's visuals are loyal to its Thief saga inspiration, but with superior character and scenery models. Best of all are the excellent lighting effects.
The Dark Mod is one of the best first person stealth games that you can enjoy on your PC - especially considering the fact that it's free, and contains tons of possibilities thanks to the level-editor that comes included.