It was completely by chance that I stumbled across Adventure Game Studio (http://www.adventuregamestudio.co.uk/), a windows application that allows you to create your own adventure game in the old Lucas Arts style.
It's a fantastic tool and, given a few months, anyone with enough imagination and some paint/photoshop skills could create something very playable. Unfortunately I don't have a few months spare at the moment, so I sampled a quadrilogy of games known as the 'Chzo Mythos' series, created using AGS by Ben 'Yahtzee' Croshaw.
If you like the Monkey Island games, you'll love them. They're filled with humour and an unexpectedly deep story arc that leaves you with a huge sense of satisfaction after playing them in order.
In today's world where all too often games developers rely on the awesome graphical power of the next gen consoles to carry a game, these games act as a stark reminder that playability and an engaging storyline are key.
You can download them for free at the following links:
5 Days A Stranger
7 Days A Skeptic
6 Days A Sacrifice