So you got a few things working out here, and a few things that could use some work-
Lets start with whats working-
Looking at the more finished sketches you have, I like your sense of color, its a good balance of warms and cools. I also enjoy what youve done with the focal points in the first and last image here, using color and light to pull the eye.
Moving on to some things to look for-
You are suffering from what many other learning artists suffer from, using photos and "stamp" a bit too much, and too literally. This makes your images feel flat and a bit sparse. On the bottom, that tree brush really stick out, when you had a great opportunity there to really make that tree frame the image more, and design the branches to lead the eye more. On 242, the goblin looking guy, The photo texture isnt wrapping around the forms. This makes him super flat, and his skin tone isnt helping, there are just wrinkles everywhere. Usually, wrinkles in flesh only occur in areas that bend or strech a lot. The more wrinkles you give something, the more it either begins to feel like a giant stiff elbow, or a ballsack. An easy fix there would be to change the skintone, and just lose some of that photo. Another example of the photos taking away from your image is the temple in the snow. The building is where I assume those monsters came from and the trees near it feel correct, but none of them have any perspective coming towards us. The monsters would be GIGANTIC if those trees are so small next to them. All in All, if you rely too heavily on photos and brushes to do your work for you, its going to cause you problems [Unless you have good foundations, in which case, you'll have more control over that, after all, its just about appearing to be good!]
So here are some things I think could help you more-
+Get back into doing foundations. Doing imaginative work is great, and its fun, Im sure if you do enough you'll learn. BUT. Studying old masters paintings, doing figure drawing, painting environments, and doing perspective construction drawings [like Industrial design type studies] of things you see every day are going to help you improve far faster. They can be fun, not always, but they can be. I've found that going back and really looking for the things I want to learn to draw has really helped.
+Dont Just do copies when you do studies. When you get back into doing them, try to recreate the image again. Construct it. Break it down into parts, and move it around in your head. Really learn everything about it. Read about them, watch documentaries, get involved and fall in love with your work
+A friend of mine once told me to try this: Have a friend give you a prompt, they can have you draw anything. Stricly pencil, no eraser, you have 5 minutes. Im sure youll find what I did. That a lot of things in that image you just didnt draw right. The real trick is to know how to draw them intuitively. But how? you may ask. Try drawing 10 of something. After you draw 10, I can assure you, you will know a lot more about how to draw it. Especially if you apply the second "+" to this one
+Every time you start an image from imagination, go get reference. A lot of reference. If you struggle with drawing or painting something, do a page of studies of that thing, then go back, and redo that. Crimson Blood Sports did this, I wish I learned about that earlier.
+I once had a teacher challenge me to draw 1000 faces. Just like what I said earlier about drawing 10 of something and learning how to make them, just tack on two more zeros to faces, and youll have a firm grasp of them. Try drawing and painting CRRAAZZZYYYY expressions too. Im sure you have that one annoying friend on facebook, like we all do, who takes selfies of themselves everywhere with a look on their face of roughly a person suffering some kind of terrible meth withdrawal. You dont even need to post them, just doing them can help.
SO, In conclusion, I just want to say, I think you have a decent start in the right direction. Proof of that can be seen by the top and bottom images. Keep working hard, and you will improve. Work hard, and work smart. Give those foundational studies some time, and come back and post them!
Good luck man, I look forward to seeing more from you!