Thank you very much for the feedback :)
If you have any suggestions for improving the tiles feel free to share them, it will certainly be helpful!
Viewing post in FREE Pixel Art Woods Tileset and Background comments
The only thing I can say that insides of tileset are empty. There are two options I know:
1. Draw some alternative tiles instead of that plain
2. Insides of earth in platformer tilesets usually is getting darker and darker when you go deeper to the inside tile. YOu can do it one or in several blocks but you certainly should add some darker colors inside. Just several examples: 1 2 3