I got used to the Unity fairly quickly. The first thing I enjoyed about it was the efficient use of vertical space, a welcome change since I have a laptop with a widescreen display, like most people that bought their computer in the last three years. Also, the left bar feels (to me) like a more efficient way to move around open applications, with the added benefit that it allows launching the popular ones that I pinned there. I must admit that I preferred the Ubuntu menu in the top left corner as it was in Ubuntu 11.04, and I believe making it the first button of the left bar was not an improvement. Clicking on a button for an application that has multiple windows and having only those windows displayed for me to choose is an improvement over using alt-tab to switch amongst all application windows arranged in no particularly intuitive way.
Using the Super key to access the Ubuntu menu is (duh) much more intuitive than ALT+F1, I don't think I need to argue about this one!. Super + shortcut keys to access shortcuts from the left tab is nice as well.
But the best improvement of all, and that was introduced first in Windows Vista AFAIK, is that I can just press Super and then *type* the first few letters of the application name, and launch it with enter, optionally using arrows to select the right one first, or pointing the mouse. This is a HUGE improvement over the previous browsing-only menu.
Placing the application menus in the top is efficient use of screen space. Getting rid of the left bar when I need for a window is good. Not needing a title bar for maximized windows is then again more efficient.
The only drawback I find in the new interface is that browsing the applications is harder than with the previous one. Before clicking on the Ubuntu menu and just browsing around the available applications was dead easy. Now I have to perform some clicks to get there. I don't care much though since typing is *so* much better.
I find that the new Unity interface makes better use of the assumption that I have both a mouse and a keyboard. I like it much better than anything else I've tried.