a horrible format for pixelart...or do you prefer to store 5mpx photos in png lmao! xd. anyway, i think:
smelt: it doesn't tead well, you didnt shade it, only coloured the fire....
mining rock: do you know anything about textures? apply it to that one...
castle walls: the interior black outline doesn't help, i would make it dark gray or so.... 2: why are you shading it roundly if they are square shaped?
your barrel: i like how you apply dithering in that icon, but the iron rings doesn't read well on the left side...
dirt/grass textures: i don't know what to say, they both look the same thing hue shifted...
dirt/rocks....:contrast...
^^
anyway...good work ^^