Yes, the compare mode has been changed … and is now much more useful in PL8.
In addition to comparing without/with geometric corrections (the Reference image in PL7), the Master, the Virtual Copy/ies, and the output file/s, you can now select any image as a reference for comparison.
To see your retouching results (before/after), try creating a virtual copy, which also works with the Loupe tool.
Just wait a moment for the Loupe tool preview to load. Then you can instantly switch between the versions. Both previews are cached.
have fun 