For the tears that drip all over; (line 12)
Poe is definitely a dramatic guy, and this image is exactly his style. When his speaker feels lousy, the entire world is covered in tears. Not jut a little sprinkle of rain, but an endless dripping flood of tears. It's a little over the top, maybe, but that's exactly the point. Poe wants us to really dig into this feeling of melancholy, to feel how the whole poem is soaking in misery. If you let yourself get into it, this kind of dramatic misery can be a lot of fun.
Their sad waters, sad and chilly (line 23)
Again, Poe wants us to see that the whole world is sad in this poem. Even the water in the lakes is sad. To drive the point home, he repeats the word, telling us twice in a row about the cold, sad water. After a point, we feel like we are sort of marinating in the unhappiness of the speaker, and that's exactly the point. This is a poem about a strange place, for sure, but it's also about a mood, about the way that our feelings can change the way we see the world. This is a kind of crazy poem, but at the same time it paints a moving picture of what it's like to be really unhappy.
In agony, to the Earth— and Heaven. (line 38)
This is the heart of the speaker's emotional world. This is the reason for the floods of tears, the sad lakes, and all the rest. He's grieving for long-lost loved ones. Losing them caused him "agony." That's a key word – it makes you feel the twisting, gut-wrenching pain of loss. It's pretty clear that his agony hasn't gotten any better, that he's still suffering the pain of loss, and that's why these ghosts haunt his dreams.