Tectonic

Tectonic's approach to worldgen is quite interesting; it makes everything look quite a lot bigger and more imposing than in vanilla, with overall larger rivers, larger mountains and more interesting fields for plains style biomes, while still keeping things walkable and not overdoing anything. Building and exploring are still not too much of a hassle even with all the new terrain generation going on.

It's difficult to describe the contents of a worldgen mod, so I left a whole bunch of pictures of all sorts of biomes to showcase it better. You may also notice that vanilla trees have been reworked to have more interesting shapes, which helps with the atmosphere and may even give you a little push to make a tree house base.

Tectonic has a patch to make it compatible with Terralith, in case you'd like to mix both.