What can I say? Over all this piece is pretty amazing. There's really no need for me to talk about how original this piece is, or how well you've managed to bring a mental image to life.
I would say your technique is near flawless, but there is still some room for improvement. You seem to of forgotten to make it rain in the lower left hand corner beneath the dragon, but that can be forgiven considering the wings may be sheltering that area. This picture would probably look better if you had shown the rain actually hitting and bouncing off of the dragon, and maybe shown the rain drops hitting the little stream? As for the mountains, I think you should probably work on trying to make them appear farther off in the distance because they seem a little too bold, especially considering it is raining and foggy. Speaking of fog, a little more may or may not help enhance the picture, depending on the how much more was added and the personal tastes of the viewer. As far as the clouds are concerned they could use a bit more work, since as of right now they lack definition and aren't very realistic looking. They seem too bright to be rain clouds.
Other than that though I'd say you're good to go. The dragon looks very realistic(never mind the fact dragons aren't real in the first place), as well as the grass and everything else. It may not be the best dragon picture I've ever seen, since there are many amazing ones, but its probably up there on my personal list of the better, borderline amazing ones.
hey, this is great--yeah it does look like it's not really raining in the lower right hand corner, but that's ok, you don't really notice it until someone points it out. great technique and keep on drawing!