I own this mouse, and must protest the rating it is given.
Sure, the mouse is comfortable and I, unlike some others here, do not have any issue differentiating the side buttons in the heat of the moment.
On the other hand, quality control at Razer is extremely lacking. After 45 days or so of use, the colors on the mouse wheel and side buttons will no longer stay synced. I can turn them off, and on again, to get them back to the same color, but this only lasts an hour or so before they go out of sync again. This problem is minor, though, compared to the performance issues.
The mouse often decides that it no longer wants to recognize vertical movement, and the USB cable needs to be disconnected and reconnected to get it working again. This is a daily occurrence. Sometimes, too, the mouse fails to recognize ANY movement, and again needs to be reconnected to start working again.
The battery life on the mouse is nowhere near the 20 hours claimed in this review, either. More like 6 hours from full charge to dead-in-the-water. This can go up to 8 whole hours if the LEDs are turned off.
Then we come to the software. Over the past 2 weeks, I have had it fail completely 3 times. The software can no longer be opened, and needs to be uninstalled and reinstalled to work again. To make matters worse, the dpi seems to set itself to maximum when the software dies, making the mouse very difficult to use for simple Windows/Web navigation....which is what you need to do to get it working again!
So, in the end, this mouse if great when it works. Sadly, this is not often the case. If it worked as advertised without the constant bugs and headaches, 9/10 would be a fair score for it. As-is, I would rate it 3/10.