Grabbed this mouse after seeing the Anywhere 2 on sale, and the old VX Nano was probably my favorite laptop mouse - decided to spend the extra couple bucks on the latest and greatest.
Tracking - Haven't tried on glass, but on multiple surfaces (wood, plastic, etc.) tracking is smooth.
Size & weight - I know this is a matter of preference, but the size of the 2S is a good size for a laptop mouse, small but not painfully so, and a good weight in a small mouse.
Smooth/clicky scroll wheel - user selectable scroll wheel for different applications.
Multiple connection methods - haven't used Bluetooth yet, I use the mouse across multiple laptops and I'm not about to deal with pairing, but good to know I have the option.
USB Receiver - Small enough that it's tough to pull out of some USB ports. Also the VX Nano had a slot to store the receiver on the mouse itself. The Anywhere 2S has no such slot.
Quality - While not exactly cheap, the 2S doesn't feel as top of the line as the VX Nano. Rubber pads on the sides seem to be a cheaper material, seam in the plastic on the back which isn't perfectly flush, etc.