It's also about detail, animation and lighting used.

All the leaves rustle and branches respond individually to the wind, the same with Trico's feathers. It's all casting shadows too.
Fallout 4 has much more detail in the open world than MGS 5 plus you can change it on the fly, tons of items to shoot or displace and bases to build. A game like DOOM 4 doesn't have to account for that kind of change in the levels and can pre-bake a lot more.







