The anatomy is the biggest issue that I can see here. The paws are too bulky, and the claws should be a bit thicker. The pads on the toes are in a proper position, but the rest of the pad should be moved further down along the paw, it looks like its on the leg. With the right foreleg, even though the left leg has a an obvious joint on the right is too straight, and its impossible to see the other joint. Its not natural for a wolf that's rearing up like that, to have its leg out perfectly straight after the first bend. The left leg where it bends then goes out to the paw is bent is too, well, crooked. It looks more like the leg was broken, rather than bent.

I understand what you were trying to do with the muzzle and face, however you went about it the wrong way and the nose stands out too much. The wrinkle is too severe on the top, and there's none at all with the rest of the muzzle. When a wolf growls or snarls, the entire muzzle wrinkles, not just the top. The left eye is in the wrong position, it should be partially obscured by the muzzle if this is in 3/4th's view. The eye shine was overdone, and improperly done. When coloring eyes its important to reference actual eye shine, rather than go with what you think is pretty. A wolf's eyes are in a different shape than that, and their irises never show unless they're submitting, are afraid, or both. The fur coming along the back of the head needs to start behind the ear, not at the cheek fur. Considering how much fluff most wolves have, this makes the neck seem very thin, and thus lack the muscle to support its head. The ears are rather ragged looking, whether this is intentional or not, wolf ears aren't shaped this way. They're round, smooth and don't end in points. Depending on the situation, if this is dominant aggression you're trying to show, the ears need to be perked and forward. If this is a fear aggression, then the ears need to be flat back, and if its fear aggression showing the whites of the eyes is okay and recommended.

The mouth is somewhat okay, do try to realize that wolves have more teeth than that in their mouths, and that when a wolf is snarling, that most of its teeth are showing as its a threat display. Most wolves have dark gums, with more pink towards the part where the teeth connect with the gums. The teeth don't really look like they're attached to the gums, they look more like some kid stuck faint blue triangles on a piece of putty.

Now for the shading. Its way overdone, little bits of fur here and there aren't going to cast a shadow that spectacular, where's your light source? It looks like its everywhere at once. Once again its important to reference actual fur, rather than go with what you think is pretty. I can see you used black to shade, rather than go with a more color friendly choice. In the future, please do go with a darker shade of the color you're using, rather than just using black. This is a novice mistake several artists make and have made.

All in all, I think you need to look at more references of wolves when you draw, actual pictures of wolves, not other illustrator's works. That's going to be the only way you can improve. It sounds blunt but I'm telling you what I've been told. Reference is the key here, and should you take my advice I look forward to seeing how you progress.