The outline is jaggy. Changing the length of line segments would help, aa-ing some parts of the outline (just a tad) would also help. The contrast in your palette is pretty low, and that combined with dark outlines means you’ve flattened your images into two 2d shapes rather than convey volumes. The door seems to be over-detailed considering the detail level of the rest. Window could use some aa so it’s not so diamond-shaped. This is a good start, but it needs a little extra attention before it’s ready for the gallery.

The door looks like it's a different style than the rest of the mushroom. Did you make that door yourself, or is it from somewhere else?

A lot of the colors here feel washed out because nearly all of them, except on the door, are very light and there's very little change in lightness/darkness of the colors.