Not sure how long this drawing took me to complete, I worked on it over three days on and off. The interesting thing is that this is my first proper dragon drawing in quite a long time, maybe even a few years.
Used 3B mechanical pencil, 3B and 5B normal pencils on A4 sized paper.
Firstly, your work with the background the dragon is standing on is well-defined. Looks like actual rocky-mountains. The mountains further out behind him, though, could use some of the same detail. Looks like you took your pencil and sketched them out, while doing some light shading.
I'm curious as to how you were so successful with the scales in this piece. They're accurate, except for maybe not really looking like they're "flexing" with his muscle structure. For example, the scales running along his wings, when they come to the corners of the wings, look somewhat like they're "plastered", and unable to move with the dragon's body. BUT, the scales running along his body have the opposite effect, looking very natural and smooth.
Anatomy is HARD with animals, especially dragons. It took me A LONNG time before I was able to understand anatomy of ANY creature. His arms and wing structure are really the only concerns I have. Arms look a bit thin on the backside of the one that's bent, and there's no "joint" in the wings, making them look stiffened.
But the detail you poured into this was fantastic all in all, but learning muscle structures in the arms and wings can make the piece look even MORE alive!
The foreground mountain the dragon is standing on is well shaded. However, the mountains in the background could use the same detail. It looks slightly like the shading of them was rushed.
The scales on the dragon are very accurately drawn, although they look too tight for the muscle flexing with the structure. The body scales look like they are smooth and flexible, but on the wings they look too dense in the ends - almost as if the skin is too tight.
Animal anatomy is hard to get right, especially with mythical beings like dragons and griffins. I'm still learning on how to get the anatomy perfect for the mythical base creatures - it's hard mixing different animal anatomy types as it rarely works out right for me. The only problem I have with this is his wings have no joint. Dragons normally either have a joint in their wings to fold them in and protect them or have their wings as their forearms in true pterodactyl style.
All in all, the detail in this drawing is amazing. The shading looks fairly realistic on the dragon and brings him to life. The only issues for me is that you need to add more detail into the background mountains and add a joint to the wing. Doing this will bring it all together a lot more and bring it to life.