Examples:
first post: all materials are completely flat, strange models of that small roofs, bump on water is very high, colour of the water is really strange, all the trees are evenly distributed without any difference in rotation or scale, leaves lack translucency, sun shadows are very sharp
night scene:
if it's meant to be a night shot with long exposure, then lights would probably have some burnt highlights but on your renders it looks like the highlights are white (?) instead of coloured, also, that ugly roof at the left, strange materials on water and leaves.
in the second project: the sky is very dark (like a stormy day) but at the same time grass is very very bright (probably bad grass material or sunlight), everything looks like made of plastic
Generally, I think you would have to spend some more time on details. I can imagine it's very hard for such complex scenes like those you posted.
