Very mature way of looking at things, Johasu. It shows you're really in this to improve. That kind of spirit is what I believe Pixelation is all about.
Anyway, your 'harsh' assessment, perhaps sadly, is very accurate in my personal opinion. However, that depends more on if you're referring to the front background layer and not the front tile layer. The front tile layer works fine with the simplistic BG layers imo. What doesn't seem to work is the detail you put in the castle on the very top, which is inconsistent with the light source, and should be more shadowed than the portion leading to the cemetery which seems to be closer to the camera and should have more of the sunlight on it from where the sun is located (and thusly be a bit more detailed to potentially blend together the foreground tiles and castle-shadowed areas a bit better -- the darker shades of the tombstones break any sense of blending the tombstone layer could have with the castle layer).
While I believe creativity in composition is important, I also think you should keep in mind both the natural laws of mass, light, repetition, etc. to emphasize the 'organic' in this type of composition as much as all other rules of composition like the rule of thirds, the rule of odds, etc. to bring a sense of dynamism to your work.
Believe it or not, you don't have to be an expert to create awesome compositions. In fact, by reading this wikipedia article, and just looking into some of the composition techniques it mentions, just in a bit more detail and from varying perspectives, you can learn a great deal about it in a short time:
http://en.wikipedia.org/wiki/Composition_%28visual_arts%29I'm still not a master at composition yet (it takes a great deal of practice on a huge variety of thumbnail-sketches to get the feeling you're going for but not yet quite sure how to express in order to achieve what you're envisioning for example), but I suggest starting small and blocking in the big shapes and colors first on a variety of different designs. Then, once you find a layout/composition/color-scheme that works for you, blow it up (or put it to the side where you can see it) and start throwing in the details and refining it. This technique works just as well in pixel art as it does in digital painting imo. No books needed. It's fun to try different things to see if they can work together -- that's just art.
Maybe I'm way off the mark here, but composition, as I've found it, is all about putting elements (such as shapes) together that work to convey a harmonious/unified sense or mood (such as the feeling a tall brooding forest might be composed of a bunch of tall and wide triangles containing various trees, forming a larger, possibly inverted, triangle, etc., creating a sense of harmony in the form of shape and perhaps color in this case). Just some food for thought.