I think that the most important new technology we have is the Incremental Garbage Collector. I’ll write an article about why it so important in details soon when I have some free time. In short this technology should reduce stutters and time spikes when garbage collector works. The problem is that now if garbage collector wants to clear some memory it just makes a pause in running program and only resume normal execution once it has finished all its work. So if you make a big complex game like we do with some kind of big open world you soon notice that your game runs not so smooth at all. Depending on how much memory the garbage collector needs to process it just stops your game for several 100 milliseconds. Needless to say, that this is really horrible for gameplay. Incremental Garbage Collector works so that instead of a single long interruption of your program’s execution it makes multiple, much shorter interruptions so that they are not so obvious during gameplay.
The age of Data-Oriented Technology Stack (DOTS) has come! Burst Compiler is out of preview and is ready for production. The current state of Entity Component System (ECS) is not clear yet but I think that this year is the year when Unity game engine becomes truly AAA game engine. Unity team works hard now to get more performance gains. Basically they rewrite entire game engine now. So if you are about to start some complex game today you can forget about GameObject and MonoBehaviour. Just use new technologies!
Lightweight Render Pipeline (LWRP) is finally becomes a production-ready in this release. Good news for those who make mobile games. High-Definition Render Pipeline (HDRP) is still in preview state until the end of this year.
Among other improvements I can mention improved lighting quality and control, reflection system improvements and GPU Lightmapper improvements.
So let's sum things over. Unity 2019.1 is the first release in this year that makes some new technologies ready for production but still a lot of them in preview state. Also the situation with new Unity networking library is not so clear to me. But bear in mind that Unity game engine evolves very fast today. So many promising new features and improvements are in process of finishing. In fact with all those new technologies Unity becomes totally new game engine.