I like the idea of the vertical tabs, but honestly, it's too much of a difference for me from what I'm used to.
I do utilize pins a lot (to pin like email boxes, calendar, drive, and other common things I log into every day), so vertical was interesting due to how many pins I have.
Almost like allowing vertical tabs to be used for pins, then horizontal tabs for "traditional" browsing would be nice. The pins already use a small icon to denote them, so the sidebar area would be very slim and not take up much space. I could quickly access my pins, but then still have the full topbar space for non-pinned tabs.