What I love most about this piece is the horse himself. He really has substance and I am a sucker for those shines, which really do look like shines on his coat and NOT weird highlights on plastic/whatever; as many people do them.

The critique I have about Murc is about the mane and tail, of course. The fox-like quality of it that people mention definitely is there, but that doesn't mean that horses can't have luxuriant tails. However, what the problem is with both the mane and tail is that I don't think that every hair would go almost exactly in the same direction, realistically. I know it took you probably a long time to make it that way, but here are a few examples of running horses with their manes flowing (rather thick ones too): [link] [link] [link]

(hope those work)
So, as you see, there IS some organization to the flow, but it's usually not quite THAT organized, if you see what I mean.

Backgrounds are a bitch for me too so I feel your pain, but I may be able to lend some advice as far as how it looks. First of all, yes, the Rainforest Ice XD It's a wonderful idea and I think would have looked great if you maybe included the texture of the dirt beneath the water in certain spots it might have made it more convincing. Perhaps puddles would have been the way to go, like this, with the texture of the ground in there: [link]

Another thing is, if the trees in the background were backlit as you seem to imply, they would probably be a lot darker, as that's the tendency of backlighting to do: [link]

The last thing I have to say isthe coloring of the foliage. The textures are intriguing and lush, but I think that for a rainforest, they may be a tad bit on the yellow side. Try making them a little bit more blue; or, if you want to make a surreal forest with warped coloring, make sure the colors work together. I'm getting a little bit of conflict from the bluish color behind the trees with the yellowish green foliage--especially because I want the foliage to be bluer!

Anyway, there you have it, my two cents. Overall I think you are making a great improvement--I've been watching you for maybe a year and a half or so, maybe longer, and I love the evident improvement, especially n the horses like this! Keep it up.