The game is built on the Source engine. The story begins on an uninhabited island, and the narrator recounts events from the past, as you slowly walk through the levels. If you have played the game, and didn't fully grasp all the details of the story, I recommend reading the story analysis done by Pop Matters, which can be found here - http://www.popmatters.com/post/164085-/
It takes about an hour to finish the game. Its an enjoyable one hour for sure. There are four levels in the game, each level will take about 15 minutes or so to complete, and they are all beautiful, with the Underground levels being the highlight. They put the Source engine to good use.
The gameplay is very simplistic. The player slowly walks (can't change the walking speed) through the levels with narration in the background. The game has absolutely no interactivity.
The main menu does not show any load or save options. There is a quick save and quick load option using hot keys, but you wouldn't know this unless you were looking for it in the key bindings. The interface is very minimal - this is a good thing for the game. I am glad they gave this option because I revisited the under ground level (the best level in the game), I wouldn't have bothered to do so without the quick save.
Dear Esther is significant in terms of giving birth to the genre. Without it, there may not be an Abzu and Firewatch. I still can't recommend paying $9.99 for this game. I got it as a part of a Humble India Bundle 8. I paid $1 for four games, and I think I got my money's worth. I would be disappointed if I spent the full asking price given that there is absolutely no replay value.