Enriched is checkerboard 4K with better shadows, less pop-in, and various other improvements to things like ambient occlusion and terrain tesselation, but the final image is slightly softer than the native one.
Native is absolutely pin-sharp, but the graphical settings are equivalent to the base XB1 (albeit with better textures and texture filtering).
You can swap on the fly, so just take a look at both and see which you prefer (I'm going with enriched, personally, as pop-in and obvious LOD transitions have always bugged me).
It's checkerboard-style reconstruction to 4k. If you look closely at the edges of the tree branches in the top left of
this screenshot, you can clearly see checkerboard-esque artifacting.