With no characters to interact with, no enemies to fight, no puzzles to solve, no way to manipulate the environment around you, Dear Esther is guaranteed to spark a thousand hand-wringing debates about what a game actually is. Can a game have none of the elements listed above and still call itself a game? Or is it enough to provide an experience to the player? Come to think of it, if you're not "playing", what do you call it?
I guess you could call it exploration. Dear Esther is great at exploration. You explore an uninhabited island, with its beautifully rendered landscapes and scattered clues to the people who once lived there. You explore the story (or stories) being told by the disembodied narrator. You explore the nature of gameplay.
More than anything, though, Dear Esther is about atmosphere. The story being told, the tone of the narration, the haunting soundtrack, the gorgeous visuals. These all add up to a singular atmosphere of loneliness and desolation. The creators have said they were influenced by Tarkovsky's Stalker -- a film that is more about creating an atmosphere than telling a compelling story.
But, although it tries, it can't escape its game roots. Dear Esther is built with "Source" engine, the same one that powers Half Life 2, and so it's necessarily constrained in the scope of its ability to tell a story and build the atmosphere it is going for, in much the same way as a book is bound by the constraints of having to tell its story through the medium of static print. As a result, its game-like artifacts are completely out of place in such an anti-game. To prevent you going too far off the prescribed path, Dear Esther uses conventions like invisible walls and insta-death points. Arbitrary rules that people often expect and that sometimes even make sense in a traditional 'game'. In something like this, though, they shatter the illusion and the atmosphere.
As a game (if that's what you decide to call it), Dear Esther a failure. As a story, it falls similarly flat, drip-feeding the brunt of the story through the same kind of cack-handed, painfully oblique passages as we saw in Braid.
As an experience, there's nothing like it.