I had a rough start as I downloaded one of the original archives. This install would throw an error when clicking on the Tools menu. Apparently the archive was updated shortly after the release. I downloaded it again and now it is fine. That was the only major issue.
When opening an existing schematic, I did have a bit of a doubt. I get the dialogue to re-map the symbols. My first fear was what that would mean in 4.0 - symbols suddenly appear in a different size and things don’t quite connect any more. From a brief look around, it seems the best is to accept the defaults. I have not looked into the details yet to know any better. Needless to say, accepting the defaults for the couple of projects I have tried this on has not shown any surprises.
For a new project like the Blinky, it went smoothly. The only thing that lost me was the renaming and re-locating the OpenGL option for in Pcbnew. The hot-key has not changed, just the name. It used to be under View. But they are now located under Preferences.
I found the explanation and now it all makes sense. Legacy (F9), the old layout canvas and will be removed at some stage. Modern Tool set (F11), is the preferred canvas and is renamed from OpenGL. This name had no real functional meaning with respect to the Pcbnew. The Modern Tool set Fallback (F12) is in case F11 does not work i.e. problems with the graphics drivers.
Once that was understood, it was clear sailing. I also noticed there is an “add vias” tool. This really simplifies things like via stitching as I don’t have to create a special footprint for the purpose.
There is more to explore in Eeschema too… a Symbol Field Editor in speadsheet format where it looks like the component values can be updated. This will be handy for making corrections etc before creating the BOM. One of the reasons I have never really used the BOM feature that much is the back and forth making corrections.