I bought the Razer Naga Epic over the weekend. I wanted a wireless mouse since I play from the couch and don't wanna get tangled up in the cords. As long as the mouse stays within 6ft of the receiver, it responds perfectly from my observation.
The 12 button side panel is great if you play MMORPGs where the command bar is linked to the number keys (top/side). If you like to use your mouse to move the camera angles and target mobs, it's great for NOT having to move the cursor back and forth between the command bar to click on an action and then back to what you want to click on your screen.
You can switch between wired to wireless pretty easily as well. Has lots of color combinations for the lights, but I don't really pay attention to that.
Tried it with Secret World (first beta weekend). Buttons 1-7 are what's used.
Currently playing Diablo III with it and it's great. Buttons 1-4 are used.
Haven't tried it in WoW, but I'd assume it'd be great for PVP since you can move/strafe while still inputting commands with the mouse (via side panel).
First person shooters aren't my cup of tea so I can't really comment on that.