I like this piece. At first glance, its well-drawn, constructionally dynamic, and thematically clear.
The strongest aspect is the color, especially in the shadows. You moved from warm colors in the highlights to cool colors in the shade making the forms really pop. I can't stress this enough; most digital works omit this technique.
Other than that, Toothless and Hiccup's physiology are pitch perfect. All of the piece's elements lead the eye to other points of interest.
One minor problem I have with the work is the water. Water is usually drawn with either reflectivity, transparency, or a healthy combination of both. This has neither making the water look opaque and milky. I would suggest drawing the water to show the stream's floor or the surrounding objects near the bottom third of the composition.
I could go on about how there isn't enough clutter for my taste but that notion is silenced by how beautiful this is. Fine job.