Dear Esther is a beautiful, hour-long, melencholy, atmospheric, interactive story. The extent of your involvement in the game is pointing your first-person view in the direction you wish to move, while exploring the world around you and listening to the narrator. The exact story, itself, is open to some degree of interpretation and this is better identified as a story than a game.

It's certainly worth playing through if you find it on sale. Alternately, this was originally a very highly regarded Half-Life 2 mod, so you can certainly pursue that option if you wish to play it.