It has a sweet spot that doesn't really fit for some. For example it is less productive than Gnome 2 if you have large monitors, lots of windows, and have multiple windows from the same app. For single tasking a handful of maximized windows Gnome shell works great, especially if using lower resolution smaller screens, and possibly fingers.
The secondary problem is they keep removing functionality and configurability, and this isn't done in public. I'm the first to admit that I actually like less configurability - I'd rather the developers made good choices in the first place, rather than just throwing lots of options over the wall and making it the user's problem. But some really annoys people - for example Nautilus just lost the status bar so finding out the amount of free disk space went from moving your eyeballs to clicking in the background, making a menu selection, having a dialog appear, reading and dismissing the dialog. I insist on using focus follows mouse, so if that ever got removed I'd be up in arms too.
The theory from the developers has been that Gnome 3 has a powerful extensions mechanism so you make it do anything you want. While that satisfies some, it is annoying to the rest of us. We don't want to extensively program our desktops - we just want them to be productive, and prior ones like Gnome 2 were productive.
I'm a big fan of GNOME 3 too, and it can be a highly productive environment. I've tried KDE, Xfce, i3, Awesome and Xmonad; I give each a proper go, getting over the initial learning curves and adjustment periods, but in the end, I find myself back with GNOME Shell and I'm quite happy with it. I don't mean to demean those projects; I think they're all wonderful and I'm happy to see them a part of the Linux ecosystem.
At the end of the day, however, the differences between desktop environments are largely a personal preference, and I'm quite happy using GNOME Shell. There's going to be people that don't like it, and that's fine. We can all co-exist.
The secondary problem is they keep removing functionality and configurability, and this isn't done in public. I'm the first to admit that I actually like less configurability - I'd rather the developers made good choices in the first place, rather than just throwing lots of options over the wall and making it the user's problem. But some really annoys people - for example Nautilus just lost the status bar so finding out the amount of free disk space went from moving your eyeballs to clicking in the background, making a menu selection, having a dialog appear, reading and dismissing the dialog. I insist on using focus follows mouse, so if that ever got removed I'd be up in arms too.
The theory from the developers has been that Gnome 3 has a powerful extensions mechanism so you make it do anything you want. While that satisfies some, it is annoying to the rest of us. We don't want to extensively program our desktops - we just want them to be productive, and prior ones like Gnome 2 were productive.