Choose Who You Are
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Divinity: Original Sin 2 starts by asking who you are, and the store makes it clear that the answer changes how the world treats you.
Six origins, or your own
You can choose from six unique origin characters with their own backgrounds and quests, or create your own as a Human, Lizard, Elf, Dwarf or Undead. Taking an origin gives you a written history to play into; making your own gives you a blank one with the same five races to work from.
The world reacts to what you are
The store asks whether you will be a flesh-eating Elf, an Imperial Lizard or an Undead risen from the grave, and promises that the world reacts differently to who or what you are. In practice that makes race a social decision as much as a mechanical one, since some doors open and others close on sight.
All choices have consequences
That line is attached to the character choices specifically, not only to the plot branches. The store also warns you to choose wisely and trust sparingly, because darkness lurks within every heart, which is a fair summary of the tone to expect from your companions and your enemies alike.
How those choices fight is covered in using the environment as a weapon. Who comes along is covered in travelling Rivellon with three friends.