I notice different things depending on the home. Some homes you walk into and before you CAN notice anything else, you're amazed at the beautiful interior decoration or maybe there is a bold theme of sorts. Another you walk and and it's, ugh, what is that SMELL? Another you'd notice "whoa, they definitely have kids" since you see toys all over the floor. Or maybe you're greeted by three large dogs. Anyway, there's always something to notice but what that is really differs.
People who walk into my house no doubt think right away "where is their sofa?" The living room is right at the front entrance but we have a weight bench and toys for DD in there, but no armchairs or sofas (much less a coffee table!) in sight. I'm not anti-sofa (quite the contrary, I love to curl up with a good book on a sofa) but one of our cats peed on the horrible 1970's sofa someone gave us out of their basement when we moved in, and we don't have the money to buy one. At this point I think I don't want one yet anyway, at least until DD is older.
When I walk into my neighbor's house, I think "wow, this is small!" (The house is probably 900-1000 sq ft, ours is 1200, but it's not just that but also the floor plan... when you walk into my house there's a lot of open space but not so with my neighbor's house).
When I walk into my mom's house, my first thought is "beautiful floors!" (actually laminate but very realistic wood grain and lots of open space, lovely) and second thought is "look at the size of that TV!" (I think it's 50-something inches).