Pixels look a lot better when you only use straight vertical and horizotnal lines for squares. Square up that window, picture, table front and stove front. Don't try anything fancy when making pixels, unless you're a real buff, otherwise it'll lower the quality. The perspective is a bit wonky, you may want to lower the angle of viewing on the stove and table, as if you were looking out of the window from that perspective, there is now way in hell you'd see the sky unless the house was 1,000 feet off the ground. Also, there should only be 3 kinds of lines you should use for the majority of work, unless you take the time to shade either side of a line (each symbol represents 1 pixel)
straight lines
.... ..|.
---- ..|.
.... ..|.
.... ..|.
diagonal type 1 lines
\... .../
.\.. ../.
..\. ./..
...\ /...
diagonal type 2 lines
|... ....
|... --..
.|.. ..--
.|.. ....
and yes, my sig is abad example of this :P but then again, im not using geometrical shapes for which this rule especially applies.