The overall feeling of Windows has changed dramatically with 7 and now 8. Before it felt like a very enterprise and cold operating system. Now, it actually feels refreshing, futuristic, and dare I say hip? Great job to the Windows team for this amazing feat.
As for Windows 8 itself, I feel like the Task Manager alone is something worth upgrading for.
I had a very similar experience with Gnome3. After months of complaining about how they completely ruined the UI and all the other flames (enough to motivate me to switch to a tiling window manager), I logged into it to see what was going on, and it looked really cool, and seemed more productive than the old Gnome2.
I suspect I would have had a simmilar experience with Windows 8 if not for its horrid use of green, but that was an early developers preview, and I will be shocked if they haven't improved the cosmetics for the general release.
As for Windows 8 itself, I feel like the Task Manager alone is something worth upgrading for.