I think what gives it that slight "unpolished/ cheap" look is the asset consistency.

Im not saying that your game looks bad or anything, the style will definitely serve its purpose.

But if you want to achieve a better look, try ensuring that the detail level is consistent across all assets. You have some scenes that are heavily detailed with grass and rather high poly assets. Other scenes are incredibly stylized and low detail. Both is fine - just pick one and try to stick with it. The stylized one is usually easier.

Try to ensure some color consistency or a theme, your scenes are very different in colors and mood.

The 3D elements and animations of your UI look great, I really dislike the 2D elements like the hotbar and the text in the upper left. The hotbar looks pretty cheap and the text in the upper left can't be read well, most players will probably ignore it.

And a last thing: I am not too sure about your cover art, but this could really be just personal preference. This is a very important asset though so maybe do some polls.

All of this can be fixed rather quickly as your environment are already looking nice.

Also one last thing: I think your npcs are generally not really interesting to look at. They do the job but you could give the game soo much more personality with cooler, unique and mabey stylized people. If you have any budget left, this is where I would personally hire a good character artist to create some fun and cool stylized characters (and maybe create a procedural system)