The music is good, got me boppin while commandin.
The first level is already moderately challenging for an RTS campaign.
The witch king seems to aggro and walk when attacked, not sure if there's a button to stop that, but it was spooky for a moment when he would turn around, and I would need to drop selection to snatch him from danger.
The mantis cloaking is a fun thing, I liked killing the dead-zone enemies with one mantis. 
This game is really cool looking too, and I like the hexagonal system you have set up, the pathing feels better than on squares in my opinion.
Good work, I'll add to this comment if I see anything worth mentioning, back to command!