I can't really see much evidence of color ramping or AA, but I would suggest some things:

- Define a clear light source (this includes casting shadows as already mentioned)
- Work on your perspective. The subject is a box plus a cylinder cut in half. You can easily model lighting and rough in some perspective lines when thinking like that - currently the circular part on the box looks out.
- Work on the design. For example, load that chest will all kind of treasure, place treasure around it. Think about different textures and wear and textures or patterns on the box. Currently it's very much "wood is brown" and "metal is grey" but you need to think about its environment and reflections too. Also the fact that someone would have designed and built it in a certain era. You could try compiling a list of reference images. Try to break away from stereotypical a little and make something different.
- Modify the palette. Here is an example (just my take on it, I have my own style), plus an example of texture and lighting on the lid:

Thanks! Gonna try and fix it up now. Do you think I should go for realistic proportions? I was kind of going for child/teen proportions a little bit cartoon-like but if it looks off it's no good

Cool. I would suggest making the tree tiles a bit more subtle. They are showing up as very repeated. You might be able to get the tower to look more interesting too by using a warmer colour in the sunlight, but I'm not sure what this piece is for / if you are using a pre-set palette.

Not bad, you could possibly improve the chin shading to be a bit flatter (less round and chubby) after looking at your reference.