What are the narrator's first impressions as he draws near the House of Usher?
The house itself, in its decadence and ruin, represents what many critics consider an unhealthy relationship between Roderick and his sister Madeline. As the narrator approaches the house, he notes the overgrown vegetation engulfing the house and a crack running along the cornerstone, then spreading out to both the top and bottom. Once inside, he hears sounds as if the house is sighing and groaning (no, it's not just the wind), and later these noises are confused with the actual cries of Madeleine as she tries to beat and claw her way out of her casket when she is mistaken for dead and buried alive. The final scene is the crescendoing "cymbal crash" as the whole house comes toppling down, when only the narrator escapes alive. Indeed, Poe portrays in a very graphic way something very rotten in the Usher household - most likely an incestuous union between brother and sister.
In the story, the narrator first sees the House of Usher in the very first paragraph. You can look there for more details...
As soon as the narrator sees the house, he starts getting very bad feelings about it.
with the first glimpse of the building, a sense of insufferable gloom pervaded my spirit
He says that it filled him with melancholy. He didn't like the way anything looked -- the house, the wall, the area around it. He says the windows looked like empty eye sockets and the trees looked decayed.
The first paragraph of the story gives many more things that made him feel the way he did, but the overall first impression he gets is very definitely negative.
“portion of the masonry had fallen...there appeared to be a wild inconsistency between its still perfect adaptation of parts, and the crumbling condition of the individual stones. The eye of a scrutinizing observer might have [noticed] a barely perceptible fissure, which, extending from the roof of the building in front made its way down the wall in a zigzag direction, until it became lost in the sullen waters of the tarn."
i.e. it is falling asunder and has cracks in it