Season 4 of Playerunknown's Battlegrounds has now started, and it brings with it a completely revamped Erangel, in addition to the new Aftermath Survivor Pass, with new skins, and even a vehicle skin for the UAZ, among other items themed on Erangel.
The game has been rebalanced, too, and there's a brand new UI with this update, so it's a pretty significant change. The biggest changes are Erangel, though, which has changed completely in many ways.
The map has brand new complexes and improved graphics, which are the most significant changes, but there's subtle little additions everywhere that add lore and backstory to the environment, something that may be a precursor to the planned PUBG single player project.
The game promises that each new season will bring significant changes like this going forward, as well as an improved patch naming scheme, with this on being named "Season 4 update 1".
You can see the full patch notes here.