Very fun! I really liked it. 

Currently there are 40 levels which took me some tries. I was VERY engaged with the game. Would love to see some more waves added.

I was unable to do anything with what seemed to be coal, and the last level I reach for Forest (I think it was lvl 5) was giving much more boars that I needed instead of more fire.

This is one of my first merge games, so I do not now if its not expected of the genre, but an ability with cooldown to merge all current inventory items automatically would be fun, like the hammer that is needed for several recipes. Like, you click a button and all the stones are merged with the woods automatically and create lots of hammers.