Absolutely love my MM. One caveat: I don't game, so I can't speak to that - maybe if I did, I'd decide the MM is not for me.
Otherwise, this is the best mouse I've ever owned, either on Mac or PC, and I've been using mouses on computers for 20 years.
The Mighty Mouse kept dying for me - I loved the scrolling, but then the scrolling thingie would die and nothing could bring it back to life. But with the Magic Mouse, the scrolling is even better - I wish the battery life was longer, but oh well (I have to change it like every 2-3 weeks, and I have the supposedly high performing Eneloop rechargeables).
I have no problem with hand getting cramped - hold it with your thumb and little finger, don't rest your palm on top of the mouse. It's easy peasy. And fast, one flick - split second, like definitely less than a second, and I move the cursor from one end of my 27" iMac screen to the other. I don't see the need for it to be faster at all - it's so fast it practically disappears during movement.
I love it.
One minor quibble: from time to time - like maybe once a month, it'll lose connection spontaneously, and I have to click to regain it.