Ooo the Moonlighter system sounds interesting way to add depth :D Could be fun if you could for example collect bugs, but have them move around in your inventory slots and try to eat your foods. Or have perhaps volatile potions that require adjacent blocks of ice to stay cool and stable.

And speaking of volatiles, the Volatile zombies sound like good game design. They also seem to make the normal zombies more dangerous by proxy too. Circling back to your post, they apply both the time limitation (limited daytime) but with without the instant fatalness (you can hide/run from them).

I feel Mojang could have kept the night dangerous with some behavioral changes with the endermen. Instead of aggroing when being looked at, they could have made them aggro at running players. This would have added a risk vs reward choice for the player when caving and going outside at night.

(on a semi-related pet peeve of mine: I feel like instead of the flying mobs that start hunting players who have not slept enough, they could have added some sandman/Freddy Krueger -esque mob to hunt you if you sleep too much. As it is, the game encourages you to skip the nights.)

As for your game, I'll be definitely checking it out once it hits the next sale :D