You will not (unless you thrash hard against the game's intentions) see everything in your first run-through.
(They left out the run button for a reason, see?) Moving into new territory is always the best-rewarded move, and therefore your choice of path is a choice. Worse: given the game's sedate walking pace, it's slightly frustrating. Precisely because the game lacks keys, switches, stars, and 1ups, it has no implicit mandate to explore every inch of territory. There are no game-mechanics associated with the choice, and a plot-diagram analysis would call them "the same place" - you can try either, back up, and go the other way. You walk along the beach a path goes up the bluff, another along the strand. So, given this interface, whence interactivity in Dear Esther? I say: from an understated but deadly-precise sense of attention design through spatial design. (Okay, you can hold down a mouse button to zoom in a little, but this didn't add anything for me and gave a weirdly non-mimetic FOV-zoom effect, so I avoided it.) Dear Esther is the elusive zero-button game. But it does - despite the absolute lack of any verbs besides "walk" and "look around". I might still hedge if the thing didn't come off as an interactive experience. It turns up regularly in the IFComp I've committed it myself. But at this point, "semi-hallucinatory journey across a lonely landscape with background story" is an established game genre. Two decades ago I was hedging and calling things like Gadget "interactive movies" rather than "games".