I think it's been mentioned but there is the big tangent between the roof and the front walrus which is distracting. There's also some smaller ones against the belt on the walrus in the background too. The walrus in the back has the same line weight as the front walrus which flattens the image. The sketch itself is inconsistent, there's a cartoony fish head on the second cabin but then really realistic fur on the walrus's mustache and realistic clouds/trees. The piece seems to lack composition, as my eye is dancing all over trying to find something to focus on but that can be easily solved eg. using arrows pointing to the main walrus? Also to achieve more depth you might want to either reduce the detail in the things in the background or lighten their lines. We normally don't see that much detail for things in the distance.
These are all fixable. So don't give up