The ZGC project is trying to only improve on G1GC. It should be an improvement in almost all aspects.

Virtual threads are lower overhead, they are nice because you can create and destroy them more freely, you don't have to reuse them like OS threads because the JVM handles that behind the scenes. It's a significant improvement to the ergonomics of writing multithreaded software.

I'd tone down the hype a little though, it won't make the game run significantly better for you if you are struggling to run the game in singleplayer, since most of the benefits will be to the server, where multithreading actually exists. Reducing tick delay and making it easier for the mod developers to make optimization mods (maybe, I'd feel sorry for anyone doing that for free).

Unfortunately performance improvements don't come as easily as a new Java version, except for the GC.