Abandonware Adventure games
Immerse yourself in a deep story and sometime a deep character. These games usually ask the player to explore fictional worlds and interact with objects or people. Some enigma will usually block the player in the story and he will have to use his intellect to resolve it.
In the Adventure genre, you may want to play ...A Personal Nightmare, 007: James Bond - The Stealth Affair, 10Rogue, 1893: A World's Fair Mystery, 2 Shot Diary. Those are just suggestions, you are welcome to download any game!