@Squirrelsize Yo! this is coming along great. Here are my thoughts:
I like the color palette it's cool and very relaxing which is really nice. I love the willow framing everything and how it feels like the willow is holding all the characters under its boughs.
I feel that you need to play with your Unity a little more. You have all the characters, car, and manor in high detail. But the environment is too flat in comparison, it does not feel cohesive as a whole.
The figures and tree especially look like you dragged a jpeg into illustrator and just applied a trace filter, and so you ended up with the very blotchy rendering on the tree. I actually really like this rendering, but since the whole piece doesn't follow that element it looks pasted together. Especially the otter in the lower left right now, it looks like a sticker added to the composition after the fact.
I would actually suggest cutting out some of the figures. I know you have spent a lot of time on them and it would suck to throw out work, But, I would simplify it down to just mole and rat in the boat and keep the manor on the hill, but cut out the car, badger, and otters. I know you wanted to show all the main characters in the cover, it's getting overcrowded and the other elements don't mesh as well. Simplifying it to mole and rat in the boat would really help this design.
I love the lettering, and the angle that it is at!
Keep up the great work! this is gonna rock and I can't wait to see you continue along.