I just got mine last week, which replaced a Logitech G5v2 that I was using for a while. After having some time with it in both general use and gaming, I'm liking the G500 over the G5v2. Although the overall shape of the G500 is very close to that of the G5v2, the grip on the G500 feels better. The ability to change the scroll wheel from click-scrolling to unrestricted scrolling is a nice feature as well.
Overall, the G500 seems to be an improved version of the G5, with a better grip, adjustable scroll wheel and additional buttons.