The G5 and the Copperhead use the SAME laser sensor so they perform pretty much identically, the only major technical difference (affecting performance) that I can see is the razer can pump its USB rate up to 1000Hz over the G5's 500Hz, though it's debatable what effective difference that makes.
I think it's basically down to personal choice on what shape of mouse you prefer. I only use my fingertips on my current Logitech mouse when gaming, I don't rest my palm on the mouse anyway and I think the symmetrical Razer feels like I could move it a bit more accurately than the G5. Other people find it uncomfortable in extended use and prefer the G5. I don't know why people are getting so worked up, it's really down to how you personally use your mouse.
So far I haven't got one yet though. They're kinda pricey and there have been so many reports of problems. At least with Logitech you always get a quality product. So I'm waiting to see if the prices fall a bit and give them time to fix the problems before I consider getting one.