Your left mouse button is useless. It's not needed, and neither is your right. Dear Esther doesn't require you to interact with these inputs. It merely asks you to walk, to explore, and, most importantly, to listen.
Whether or not you want to play Dear Esther shouldn't be up to whether it is fun to play (it isn't), whether it's got some great mechanics (it doesn't), or whether the difficulty spike is unfair and frustrating (it's not; there isn't one).
Dear Esther depends entirely on two things from its players: an open mind about what exactly constitutes a game (and whether that is something you'll get hung up on) and an appreciation of its bleak, ambiguous narrative that requires you to decide its meaning rather than be spoon-fed it.
In its formative stages as a Half-Life 2 mod, Dear Esther called itself a ghost story. It's not. The desolate island it has you explore is certainly creepy, in the same way that anything abandoned plays with your fears. This world has its own history, and not explicitly knowing its background is enough to thrill. There are light touches, and unanswered questions, that feed into this lack of knowledge, which in turn heightens our fears, but it's not a ghost story in a traditional sense.
Well, maybe it is. My Dear Esther isn't a ghost story. Maybe yours is.
You walk, and randomly selected chunks of narration ambush you when you trip invisible, intangible tripwires. Whereas something like The Path actively encouraged you to deviate from the path, and find its obtuse dioramas, Dear Esther doesn't give you that option. Everywhere is the path, and everywhere leads where you need to go. There's only really one direction to travel, even when it seems like there's more.
I'm dancing around talking about the game; it's not easy to write about, because if you go into any depth you've ruined the thing. Delve into the story before experiencing it and your perception will be coloured, and how you perceive it is half the fun. Discovery is such an important part of Dear Esther, especially when everything is so phenomenally pretty.
What The Chinese Room has done with the Source engine is a miracle that even manages to put Valve to shame. Comparing the original mod to its current incarnation, Dear Esther is now breathtaking to observe, morose and bleak but absolutely breathtaking. It manages to capture that feeling you have when you're forced to go for a walk with your family after Christmas lunch and you realise that, well, nature is pretty bloody beautiful. It's cold, and there aren't many leaves around, but gosh it's pretty. It feels like a revelation.
Dear Esther is that same revelation, slipped innocuously into a videogame.