From what I recall, Badlands doesn't look too technically challenging, they've just got amazing art.
Usually it is a mix of art assets, physics assets (often corresponding to the outlines of art assets), animation assets (that say how they move), audio assets, code that makes the pieces do the things, and map/level assets (telling where the other three belong in the world and how they combine together)
For the platform worlds, building blocks are common, as are artist-drawn collision maps that describe the footprint of objects or the shape of areas that can be navigated. The two can even work together, an artist draws the artwork for platform segments (often both endpoints and some repeatable middle segments) along with the collision shape for them, both can be placed by designers in the map or level data. Or if they prefer, artists can build a more complete environment with an environment-wide navigation mesh, but this has drawbacks because it makes for enormous graphics files. A small number of objects placed many times takes up less resources than an enormous world. But for some games and some levels having a fully-composed large element can make sense.
Games often begin with ugly building blocks, gray/white/black boxes and spheres and arcs, and other placeholder art until midway through development. Artists do their magic and replace the platform levels still act the same with blocks and boxy platforms and other shapes, but the art makes the world beautiful, and items appearing in the foreground and background don't affect gameplay but make the game come alive.
