Hm, it's a tough one. Especially since I can't really rationalise what I'm seeing in the image. You said 'swamp' on dA, so I therefore assume the convolution is intentional. It's not a bad thing, though. It just makes it more difficult to describe elements, I suppose.
The part that sticks out to me as being 'the worst,' is that little hill-type thing at the bottom. The issue is that it seemingly has the greatest range in values, whereas the much more carefully detailed background seems to, in most areas, stick to darker values, and therefore I seem subconsciously less interested by it.
The problem with this is that it really draws my eye, and I feel like, once there, my eye doesn't have a lot to look at -- especially when it's juxtaposed upon such a finely detailed background. The biggest 'branch' towards the left of the hill, is especially noticeable. It just juts out rather crudely, and the fact that it almost has this 'black outline' of shadow just highlights it further. The entire hill does not appear to be as carefully rendered as the rest of the image, and that's a shame, because the background is really nice.
Those black things on the hill: are the creatures, or just more details? They also draw my eye, but I do not know what to make of them. They do not make much sense as anything other than characters placed into the landscape, but they are difficult to make out. Therefore, I can't say they look as though they belong in the image, either.
That's about all I really notice right away. Otherwise, it's quite impressive.