For me, Dear Esther was worth the buy. It was a unique experience. The thing is, there are multiple routes through the game and every time you play it you're likely to find something new that reveals more about the story. The audio is also randomized, so you might get some part of the story you didn't hear before. The visuals are phenomenal. An aesthetic masterpiece. I usually care more about gameplay than visuals, but in this case... everywhere you look is like looking at an incredible photograph.
But I actually came here to mention a different game.
There's this game called Proun. I haven't played it yet. It looks really fun though.
You can get the game here for as little as $1 (pay what you want though):
http://www.proun-game.com
There's a trailer for it.
There are even some custom tracks for it, and I'm sure more will be made.