From Shelob's Cave :: Pixel Art Detail

Looks great!

Some ideas:

All the reds are the same hue, or almost. Would be nicer to shift them, for instance have the dark reds go a little bit towards purples.

Distant outlines are unnecessary, the depth feeling would be improved without them (plain, Mt Doom, mountains).

Distant clouds look like a cave, and Mt Doom smoke itself looks like the foreground cave ceiling.

Left lava flow is not as good as the others and probably unnecessary.

The bend in the road looks strange, should be flatter (foreshortening).

And, isn't Mt Doom supposed to be higher than Sauron's tower? (long ago read, don't remember!)

I think it's good that way except that empty area on the right should look like dark plains rather than hills/mountains/clouds as it appears to be to me.

Good work :)