5 Days a Stranger is the first game in the Chzo Mythos, an excellent series of games produced by the newly minted internet darling, Ben "Yahtzee" Croshaw. You take control of Trilby, a cat burglar, who chose the wrong house to rob and must now find his way out whilst avoiding the various hazards and the mounting piles of corpses.
It's a fairly straightforward point and click adventure game with the player choosing various ways of interacting with the environment with the mouse. It's a tried and tested formula and it works well here.
The storytelling, however, is where the game really shines. The house itself almost becomes a kind of enemy, and the longer you play, the more claustrophobic and tense you get. It reached a point where I had to physically stop playing the game, go outside, and sit in the open air for a few minutes before I could continue. The characters themselves are very well defined and react in believable ways to their predicament with some accepting it, some attempting to fight their way out, and some simply denying the entire thing. It's very engaging, and it gives the game a kind of credibility that is often lacking in adventure games.
Sound-wise, this is one of the few freeware games where the sound not only helps, but becomes a major part of the game itself. The music for when things go wrong is a jagged, repetitive piercing noise, and it jars you from the quiet unease that you've been experiencing and places you into full blown paranoia. It's amazingly effective, and losing the music would mean losing a substantial part of the game.
5 Days a Stranger is an amazing game and should played by anyone even slightly interested in the horror genre, adventure games, or games themselves. I highly recommend it.