What impresses Huck most about the Grangerfords' home in The Adventures of Huckleberry Finn?

I think what impresses Huck the most about this house is
how wealthy the people who live there must be.  It is a very nice house with lots of
rich stuff in it.

When Huck first goes in, there are people
pointing guns at him, but he still notices how nice it is.  He says that the parlor they
go into is big and it has a new rug.  If he notices how nice it is in that kind of
situation, it must really be nice.

Then, the next morning,
he thinks a lot about how nice the house is and how it is just as nice (and nicer) than
houses he has seen in towns even though it is a house out in the
country.

So he is clearly impressed by how nice and rich
the house is.

You can find more details in Chapter
17.