i had the g502 for a bit when i was thinking about upgrading to it from a deathadder. i swapped back to a new deathadder but i can let you know my thoughts on it.
all in all it was a very solid and responsive mouse. the buttons were all in well placed easy to press locations, weight was good, build quality was good, the software was easy to use and the sensor was perhaps better than the deathadders.
the reason i ended up returning it and going for another deathadder is because i am so used to wide mice and the g502 feels a bit thinner due to the shape of the right side which caused my pinky to curl under while grabbing it which ended up being uncomfortable to me. sure i could have changed my grip style but that was part of the reason...