So, I have to say, I like it when UIs try make things as simple as possible. I was perhaps a bit sceptical of GNOME2 initially (more cause of its crashiness), but the way it tried to simplify and de-clutter the UI was great. Further more, it was great for non-technical users.
I'm not sure GNOME-Shell sticks to the simplicity philosophy. Some common actions seem to be *very* hard to discover, requiring you to move a pointer to a special place on the screen, or to press special keys to change the mode of the UI. Of course, I'm just one user and not a very normal one, so I'd love to read an objective, metric-driven HCI study on how GNOME3/GNOME-Shell compares to GNOME2.
If I still had GNOME2 users, I'd be quite hesitant to move them to GNOME3, because its such a massive change. Some older users particularly would need a lot of hand-holding to cope, I'm sure. However, it's a moot point, as I no longer have such users - they've all gone to windows in the last few years. Driven there primarily by desire for Windows applications.