My personal observations. I know this is a beta (alpha really?) and I know things will change for the better (I hope), but some observations from the field.
1. macOS is starting to suffer the same bloat as MS Windows. Features nobody has asked for, ever. I don't have any reason to give my people voicememos, podcasts, tv or anything not work related. Make this stuff optional. A nice checkbox will suffice.
2. Intermittent, random program failures that may or may not be duplicated. Music (yeah, it's on MY private machine) is a prime example. Some time it works, some time it just sits there. A gigantic step backwards from iTunes (which had a number of its own problems)
3. It's SLOW. Let me repeat that, IT'S S-L-O-W. The people I have who are testing this O/S now have Mojave loaded in VMWare so they can get work done in a timely manner.
4. What is with "syncing" iPhone in Finder? Who's brilliant idea was that? I'm going with the same person who thought removing 99% of the functionality from what was a relatively decent (iTunes) program and making it a, to borrow a British term a doggies dinner.
5. LIke everyone else, I'm waiting for the third macOS iteration in 2.5 years. It sure will be nice when it's 65% functional.