The biggest change is audio, but also there have been pretty stout changes to the lighting system. HTC had gotten the game to the point where expanding into improved lighting and audio were a great idea to improve nearly every aspect of the game.
For instance, the terrain. How many people have noticed that the islands of Mindanao are no longer roughly hewn and craggy looking? Now you have rice paddies, corn fields, apple orchards, palm trees, rows and rows of kale, and banana trees. The terrain interacts with your vehicle in new ways also.
The lighting works so well now that we already have people complaining about vehicles being impossible to find. It is even more important now to have smoke capabilities to mark locations. I suspect that once all of the current bugs get worked out that the next level to shoot for will involve improvements to troops, but that's just my opinion.
The audio system is so involved now that you could spend years, literally years, creating an immersive environment. The incorporation of the speed of sound limitations have also improved ground battles, because a gun report is now just a hint to the source rather than a definable physical location. The sounds also change, or can change, by location as well as time-of-day.
Yes there are a few problems, but the team is working hard to get those sorted out and fixed.
And then there is VR. Not a fan, myself, but I have a brother that thinks very highly of it.
