Quality of Life
There is none. No tab dragging between windows. No history shortcut. No alt hotkeys for websites. No dragging completed downloads to your computer. Old-people sized interface. Smooth scrolling at a snail's pace. Pressing enter in a form doesn't always submit. A solid two seconds before a page starts to load. The spatial navigation is nice though.
You can make your own history shortcut. That said, one is sure to appear in the panels in time.
Tab dragging between windows will also be implemented when there is time to write the code to do so. The main hurdle, it seems to me, will be the fact that Vivaldi windows consist web tech, not native elements.
You have the option to shrink or expand the "old people" interface in tools/settings/appearance/user interface scale (an option, btw, which no other browser offers).
Smooth scrolling is at the default Chromium pace. This may change in the future.
I see no delay with page loading here. Period. Your system resources or 3rd party AV client may slow things.