Dear Esther : A Source Mod Ghost Story (v1.1)

Quick summary:
This widely-praised Source Mod for Half-Life 2 is an interactive ghost story told in the first person point of view.

File info:
223MB compressed zip
501MB unpacked
Version 1.1Description:
A deserted island... a lost man... memories of a fatal crash... a book written by a dying explorer. Dear Esther is a ghost story told using first-person gaming technologies. Rather than traditional gameplay, the focus here is on exploration, uncovering the mystery of the island, of who you are and why you are here. Fragments of story are randomly triggered by moving around the environments, making every telling unique. Features a stunning, specially commissioned soundtrack. Forget the normal rules of play; if nothing seems real here, it's because it may just be all a delusion. What is the significance of the aerial - What happened on the motorway - is the island real or imagined - who is Esther and why has she chosen to summon you here? The answers are out there, on the lost beach and the tunnels under the island. Or then again, they may just not be, after all...

Installation:
Extract the Zip file to the Steam_steamapps_SourceMods folder, typically under "C:_Program Files"

For example: C:Program Files (x86)_Steam_steamapps_SourceMods_Dear_Esther
Then, (re)start Steam.
In addition to this, you will need to have the Source SDK, which comes with HL2 or HL2 Deathmatch.

Website:
http://www.moddb.com/mods/dear-esther