Isn't Ill Borne a proper sequel?
※本作は『単体動作可能』の超大型拡張データになります。
「ゴブリンの巣穴」(RJ291561)を持っていなくても、最後までプレイ可能です。
「ゴブリンの巣穴」を持っていると、ゴブリン無双プレイ可能です。
From the store page.
For those too lazy/incompetent to use machine tools to read:
This work is an expansion pack which can be run on its own.
Those who don't have the base game can still play the game all the way to the end.
Those who do own the base game can blitz through the content as they can import their existing nest from the base game.
I don't consider it a sequel when
1. The mechanics are almost exactly the same as the base game.
2. There are links to the base game in the narrative.
3. I can bring over my 300+ generation goblins and literally have no issue smashing through this game's end-game content on my first run.
Some can see ILL BORNE as a sequel, but the official store page claims it's a standalone expansion so I'm going with that.
Others can interpret it as a sequel should they see fit, it's not going to be a key decision maker in whether or not the game is worth playing.