I've recently spent a couple of months using Gnome 3 in Fedora and a few weeks using Gnome 2 in Debian Squeeze, Now I'm using Gnome 3 again in Debian Wheezy. Switching from the new to the old and back has given me a good idea of what I like or don't like in Gnome 3, and what makes life easier or more difficult using it.
Overall, I much prefer using Gnome 3, which puts me at odds with a lot of people who have written about it. What I love most is the minimalist elegance of layout. Gnome 2 just looks 20th century while Gnome 3 looks 21st.
I have loved the Gnome 3 shell since trying it out in Ubuntu three years ago. It's a funky way of seeing what windows you have open without taking up space for a second panel at the bottom of the screen. I've never missed the minimise button, although I can see that the bottom panel is an efficient way to switch between applications (as long as it's not too full). The Alt Tab switcher in Gnome is a far nicer way to do the same thing; my only criticism here is that the Alt Tab combination is awkward: I'd like to be able to bring up the switcher with the mouse, perhaps by right clicking the Activities button?
I was less enthusiastic about the applications launcher in Gnome 3. As somebody pointed out, the paradigm is a throwback to the days when everybody had their desktops covered in application icons. However, what I've come to appreciate is the search function: type the first few letters of a application and you're usually left with just the launcher icon for the application you require. When I came back to Gnome 2, finding an application through the menu system actually felt quite unwieldy.
On the other hand, finding system settings in an icon-based paradigm seems less efficient. Maybe it's just memories of Windows Control Panel.
I like the new taxonomy of icons in the Gnome 3 Activities Window. Gnome 3 has three separate areas where the icons can go, with a
rationale for each: applications in the dash on the left, system
settings in the system tray at the top right, and notifications at the
bottom of the screen. At lot of Gnome 3 extensions seem to be trying to get away from this taxonomy and back to the old Gnome 2 paradigm (which itself dated back to early versions of Windows) but stuffing the top panel full of application and notification icons. To me that's a retrogressive step, and I hope more users come round to the new paradigm. I think it will help when more Gnome 3 applications use the Gnome 3 notifications areas consistently and as they are intended to be used.
There's also some work that the Gnome 3 project needs to do on notifications: new email and IM notifications for example need to be permanently visible so that if you're away from the computer for a few minutes you don't miss them.
This is why I like Gnome 3 more and it makes life easier, which is why I prefer it. I missed Gnome 3 when I was back in Squeeze, and a year seemed a long time to wait to see Gnome 3 in Debian Stable. My present set up seems ideal. I can use Gnome 3, whilst always having Gnome 2 in Squeeze to fall back on. I hope more people come to feel the same way, even if many Gnome users currently don't.