Hmmm so i get what you mean, i think it just lacks some main interesting feature. So something that immediatly catches your eye or something. For instance the sky looks very cloudy so maybe you get add in some thunderstorm or some lightning bolds. What maybe also contributes to the "uninteresting look" is that it has overall a very low contrast and just a lot of really dark grey values. Doing stuff in greyscale doesnt automatically makes thing boring thats not what im trying to say but i think you can just use a bigger value range, this would probably make it more intersting because you could hightlight certain parts and you would just have more contrast. I dont know how finished this is supposed to be so i would assume that if you would completly finnish it that you would get some harder edge work at some of the towers because the edges are sometimes washed here, even if they shouldnt be. At this stage you could probably also add some more detail, so it would look more natural. Overdoing detail is obviously unnecessary but you could for instance carve out some single stones at the sides of the towers, because right now they look like some perfectly geometric cylinder shapes, which would probably not be the case in real castles, because they built stone after stone and some may be worn out already over the ages. Oh and also the background looks a little boring because its such a flat land. Maybe you could add some mountains or forests there.