Great work here! There is a bit of an error in the proportionality of his muzzle. (Too stick-y-out-y.) Also I love how you shaded his neck piece and boot-things. They really look truly shiny! Another tip for you to keep in mind is to make your lines not all-black like that. It sort of lessens the impact and makes it look less interesting.
in Sai there's a tool called the binary tool (or with me it's the legacy pen for some reason) and if you use it it can make the lineart of a picture look like it was done on MS Paint or something! Here's an example I did for one of my recent pictures: [link]