Recently I've been playing a fair few free Flash games on Kongregate. It turns out that a few of the ones that I particularly enjoyed were made by the same person - Gregory Weir. These games were:
How to Raise a Dragon - a very open, branching interactive story with a lot of player choice - very charming. (The image on the left is from this game)
The Majesty of Colours - another branching game, but this time more open to interpretation - quite beautiful.
The Day - an interesting experiment in the separation of goals - plays as an adventure/collectible card game - the narrative unfolds in a very clever way.
Gregory Weir also keeps a blog - Ludus Novus - with some interesting writing about interactive art. I recommend paying it a visit.