I've been testing the betas since beta 1, and honestly, I am not a big fan. And before anyone chimes in, yes I've been sending in feedback.
I like the concept of the new interface and appreciate Apple recognizing that the current UI is getting a bit stale, but the execution has not been great. There is still a huge lack of contrast b/w foreground and background apps, the transparent menubar still bugs the hell out of me, and certain app icons still look very amateurish. On top of that, there are a ton of technical changes behind the hood that will break a fair number apps (at least at the beginning). I'm not complaining about those technical changes by any means, some of them are really important and will increase security and stability of the OS (such as depreciating kernel extensions), but there are going to be a lot of growing pains with this OS. Also, I'm still bitter that Apple is getting rid of the "Network Utility" program. I know all of it's features are available via the Terminal, but Network Utility was (and still is) a really convenient place to access all of these tools and it has a great interface.
As it stands, I will definitely NOT be upgrading when it is first released, and I'm honestly not sure when I will upgrade. I usually wait until at least .0.1; but with the interface changes and various programs needing to be updated, I have a feeling I will be sticking with Catalina for a while longer.