Ok, most of this is personal suggestions, and not hard critique stuff, so take it or leave it if you want.
For the first one I'd make it so the front and back cover blend between one another. The street, sidewalk and brick wall are seamless, so why not the rest?
For the second image, the perspective is off, but it probably doesn't matter as much. Also it looks like the street in the background isn't lined up (it changes height between the two buildings on the left.) Also it looks like the building in the background next to the tree goes out into the middle of the street.
The next two are great.
For the cd cover I'd maybe have one or two white/highlights on the text to make it more visually interesting like the logo on the cover.