Hey, KNIME Team!
I had no issues with switching to the modern UI preview, however I do- have some with what is in it, or, rather, missing (as expected, right 
).
In general, new modern UI indeed feels more modern, which is very welcome and expected improvement. I love
- the stepless zooming
- the infinite canvas
- direct renaming and adding ports to metanodes is a much needed improvement
- node action bar - well, nice, but I have no use to it, as i am anyway using keyboard shortcuts; however, popup action buttons is a big step for those who use context menus.
What I was not too happy about:
- strange looks of metanodes, the dashed-contoured empty boxes (but no biggie)
- entering metanode does not open a tab, but switches whole view. I liked tabs
- exiting metanode automatically zooms out whole workflow. That’s annoying.
- could not see the old way of checking node data output. The preview pane is rather useless - no table [column metadata] info, no sorting or lookup
- could not see any (!) way to see image outport contents (Python view)
- the new node lookup - while I appreciate the “natural” looks of nodes, I had no issue with the old, list style lookup. Additionally, the old way pane was resizeable, new one is fixed and takes up lot of space on screen. Lookup itself has a little bit improved, however.
- top bar with execute all buttons and such is another way to take up space on screen with little need, it would be good to have possibility to disable that bar. May be a personal preference, but I always want as much as possible screen space for the actual workflow.
But all in all, appreciate the effort, and eagerly waiting for further improvements. KNIME is a beautiful tool for accomplishing amazing things!