I haven't touched the terrain code in a while because of other priorities, but now that I've begun working harder on code for the map item, I can share what has changed with you.
Previously, the terrain generation was very basic and nowhere close to where I wanted it, it was only a bunch of island blobs that go on for miles into infinity. I was experimenting with hardening the generation of the planet's foundation in order to create a massive surface to the planet. Sky islands still show up in the sky, but now there is no sky below the surface of the planet. The ground below your character is all blocks that are either spawned as one of the 3 selected blocks for that planet's biome, blended around with perlin noise, and caverns that sprawl around, all relying on noise. Each planet has a slightly higher or lower density of caves and caverns, some with very massive open spaces, and others with the occasional bubble of air underground, as well as the sweetspot in the middle where caves naturally spawn.
There are only blocks that spawn underground, no air blocks, so when you explore caves the open spaces are dug out blocks with backgrounds, as can be seen below.
Also, the spawnrate of monsters and quests increases as you go deeper, for some interesting planet endgame ideas. The same goes for when you explore higher up in the planet, in the outer reaches of the sky islands.
Also, the character saving system has been finally added! The default character you start with (although characters will probably be premade in the vanilla version) is "Explorer." When playing with a character, you play as you normally do, then as you leave a planet, it saves your progress. Any player items you were holding in your inventory can be selected at the character select menu in order to have the game prompt for a new character. The player items in Generantis can be used to make new characters that you can name and play on.
That's all for now, stay tuned for more updates!