The first thing users are going to notice is the new UI. The alpha build use to include both the old and new UI so users could get use to the changes. That option seems to be gone with the beta builds or at least I haven't been able to do it yet. I'm still not sure I like the new UI but I'm sure it will grow on me. You can still create your own programs but you can no longer make custom widgets.
Many of my HG programs are going to require some modifications to work with the newer builds but that is due them having custom widgets
The new HomeGenie builds are mostly 64 bit so you need to be sure to install the correct build.
If using a pi older then a 3b+ that means you can't use the net core builds. I've not loaded up a core beta (64 bit) build yet but hope to do so soon.
Older HG backups do work with the new build so that does save alot of time.