(You should number your pictures)
1 : It doesn't really show anything. "What's the subject? What you've wanted to show? You think you've succeded?" Ask yourself those questions, with every picture (except abstract ones), it'll help you.
2 : Nice technically, but it doesn't make me feel a lot.
3 : Lacks of contrast, I think. Sepia is maybe not the best choice. Have you tried B&W?
4 : Same as number 1.
5 : Make the horizon horizontal
Angled (not sure of the word) horizon mostly deserve a picture, except when the composition justifies it (but it has to be a very dynamic composition, which is not the case here). Try also not to center the horizon : giving more importance to sky or ground (typically 1/3 and 2/3, or 2/3 and 1/3) gives the picture something more aerian, or telurian.
6 : Very nice ! Here is the horizon at the bottom third, and I'm sure people prefer that picture
(not only for the non-centering, I guess). Exposure, colors, everything is good.
7 : Good contrast bewteen red and blue (which are opposed colors). The angle formed by the plane with the horizontal is too less pronounced (or too much). A 45° angle had give it more "violence". A 0° or 90° angle had give it more peace. Try to rotate the whole picture 90°, in every direction, try to mirror it, etc... You'll see that there are some results more dynamic than others. (The plane with the nose down should be one of them). Also notice that going to the left means "look to the past" and going to the right means "look to the future" (our reading goes left to right, that's why. In Arabian society, it would be the otherway)
EDIT :
8 : That one is very well exposed, but it is also centered
