I really like the work you've done on the concept sheet, I think some of those thumbnails work better because they really focus on the shape of the octopus with the surroundings taking the second read. I think this sketch^ has kindof lost that strength, whilst I'm sure it will be less of an issue when detailed, the octopus still looks more like a background element. Another thing is that there are quite a few strong vertical lines that spoil the beautiful curves of the octopus limbs, the hanging foliage is not so much of a problem, it's more the right hand edge of the main octopus and the foreground structure on the right. They kinda break the flow of the image which could otherwise be very strong since the eye is lead around via the tentacles.
I think the third thumbnail on the concept sheet is the strongest, simply add a few foreground elements, be it simple terrain or some other tentacles. The last thing I'd say about basically all of the sketches is that the distant background structures should really be smaller and not reach so far up into the image other it breaks the sense of scale.
Sorry if this sounds like I'm just giving criticism, I really love this concept and your concept illustration looks great, good luck finishing it!
