Sorry, didn't see your post before.
The shadow of the tree is as I explained before, a combination of a diffuse shadow from the whole sky (right below the tree) and a direct shadow from the sun; only it's bad because I didn't make them diffuse enough (sky) nor hard enough (sun), it would have needed more indepth work on the palette and so on. Photo refs: 1, 2 (not exactly what I had in mind).
For the ground I removed noisy grass detail in the bg and then tried to doodle a more generic impression of faraway paririe, obviously I failed here too! Looking towards a low sun, grass would cast long shadows, as would the slightest terrain raises too. The idea being not necessarily realism, but how to convey the feeling of a sunset prairie without drowning in noisy detail. Refs: 3, 4.
I did consider a mountain shadow, but it would have to be in the upper bright corner of the grass, and would be dark and narrow.
Anyway, this edit was just a pointer, nothing literal should be taken from it ;)
And, thanks for the favs! 
Thx,
I tried to position everything so that none of the objects get in each others way while still trying to maintain the focus on the tree.
The only things I adapted from your edit are the more yellowish hue range of the sun, the necessary raise in contrast and the shading on the tree pointing at the light source, mostly cause I didnt get most of the other stuff. I'm mostly confused with the shadow the tree is casting it looks like its a combination of a light source nearly above the tree and a light source with an angle of less than 45 degrees. The ground is also confusing to me, is the darker part the shadow cast by the mountain?
Good news! I love the new start =)
Here's that edit btw. Very rough of course, just a few pointers.
Have fun!
Read quite alot of the further linked articles(elements/principles of art and many more) realizing that the fundamentals are flawed I decided to start from scratch and thus I "reopened" the WIP thread : http://www.pixeljoint.com/forum/forum_posts.asp?TID=13320
I've been drawing/pixeling my whole life but funnily enough I've never attempted to sketch anything from life, maybe I should start doing so.
The set of skills required by an artist can indeed be aquired through practice, this doesnt apply for the mindset though.
Composition: an introduction! There seems to be good links at the end, I didn't try them.
Composition is important in at least 2 respects: readability, and 'viewer satisfaction' (for want of better words). Yes, unhappy alignments can compromize both. Also as FrostButt pointed, sets of lines and other elements direct the viewer's eye either towards the focus of the piece (good) or outward (not so good). At a higher level, it would also have to do with imparted meaning.
I'm not sure of the meaning of your next question. An understanding of perspective is certainly helpful, although in a piece without angular objects it's is not that critical.
You're right about the shadow, but consider that this landscape is lit as much or more by the whole sky than by the low sun. So a diffuse shadow should darken the ground below the tree.
Anyway, sometimes true perspective or light can be bent to fit the needs of composition!
I don't believe in 'incapability as an artist'. At least nothing that practice cannot fix! Do you sketch, from life? That helps a lot. The point is learning to see more than to draw.
Thank you all for your thoughts,
@Manupix
Composition, could you sum up the essence of it in a short statement understandable for a simpleton like me, I mean like the essence/purpose of shading is building up 3 dimensional forms.
Regarding the upper tree I see what u mean with the curve, but I dont get how it destroys the impression of depth, does depth generally get compromized if foreground objects and background objects align? Also is there a way to maintain a certain level of "objectivity" in terms of depth/perspective,while pixeling the piece, to unravel such issues on my own?The color issue can be solved due to further desaturatung the background while saturating the foreground, I guess. About the cast shadow I assumed that light if the light source is distant enough travels in parallel lines, thats why the I shaded the tree that way and thats why the shadow in the piece is far beyond the tree, guess that doesnt work that way.
An edit would be very helpful, I was going to work on it this weekend anyways.
Regarding my missing pieces(short version): What happened to them is my incapability as an artist.
Interesting texture experiments. But I agree with Frost Butt, you need to give your piece a solid foundation (composition and shading) before you start working on that level of refining.
For several reasons, the upper part of the tree seems flattened out on the faraway hillside, this kills all depth in the piece. Among reasons are: the treetop curve and the hilltop curve are overlapping; the dark green blends wioth the dark blue; the leaves and branches don't cast a shadow on the ground; the tree shading is not realistically indicative of a light source.
I might try an edit later.
Also, what happened to the rest of your gallery? 
I like it but i feel the orange on the tree makes it look like it's on fire though XD
The grass creates a cool effect on the eyes. The style is pretty great as are the colors, but that white on the sun is too distracting. Also, the composition is really unbalanced and not pleasing to me. In the top left, the cirular thing points us down and right, but the tree interrupting seems too abrupt
I liked this one. Nice.