This is all I'll ever need. I'll tell you why..
I don't like "ergo" mice. See how on the MX, the thumb is supposed to somehow rest under the index finger? Having a dome-shaped mouse allows your hand to lay easily on top of the mouse without any contortion. Not only that, wireless mice are too heavy. As an FPS player, I need a light mouse and the IntelliMouse Optical is like a feather. Special features be damned if the mouse can't do what its supposed to do, which is point and click as accurately as possible. I feel like heavier mice require more muscle control to get them moving and then to get them to stop where you want them.
Not to knock your mouse. I just wanted to add a different opinion to the mix.