Super good! Super hard! This game is very highly polished, and you were able to accomplish an impressive amount! It's just hard to see it because the game can be pretty difficult from the get-go. But I really wan to play more and get upgrades!
The gems are nicely integrated into the various systems of the game--they help you see where the humans have been, they act as a sort of timer, and the ones you manage to save act as currency. The desire to hoard and protect them is very compelling to me.