I think that your sprites will look better (especially bigger ones) if you commit to one source light point. It’s best to keep it at the top, especially since you already have shadows at the bottom. This should be applied to buildings as well.

Adding some shadows under the characters (in the same way as you have done with bosses) will make them more grounded visually.

Also, dark text in your main menu is not very readable against darker gray, even though you have those brighter outlines. It’s worth that you experiment further with that.

Here’s a fast edit with some suggestions related to the above light source position comment (I didn’t want to change the designs just, just give suggestions). I hope it will be helpful.

Demolitionist:

These units strike the ground with their hammers damaging everything nearby.

Mine:

All adjacent unit special abilities are activated 20% faster (doesn’t stack).