Gnome 3 is the "Windows Vista" equivalent of Linux. It looks better? yes, but at what cost? it takes a lot more resources.
I hope Gnome 4 pulls a "Windows 7" and comes back as a modern, optimized DE, with a "no 50 watts GPU/CPU required" mode for people that don't want/have it. Until then, Mate desktop it is.
You still are talking about a x86 architecture with a discrete GPU.
It would be nice if it worked fast with no GPU at all like Gnome 2 did, so it can be used in Virtual machines, OSes with crappy drivers (*BSDs), weird architectures (MIPS, ARM, etc.)
Gnome 3 sacrificed all that compatibility to gain some nices graphics, I think it's not worth it.
You know just how hugely powerful an i5 processor is? the "no graphics card" that you actually have inside your CPU is more powerful than the latest gamer graphics card from 5 years ago. And consumes a lot of power too.
Gnome 2 ran quite fast on a 500 Mhz ARMv5, 200 milliWatts idle. Yes, it is a niche application, but it shows just how much hardware (and batteries!) Gnome 3 needs.