I have the G502 Proteus Core and it's really good. I have it for quite some time now and I can't really say there is anything I don't like about it. Maybe the underside of the mouse should be a bit higher than it is, because it's dragging it's underside plastic surrounding the sensor on my Razer Goliathus pad and the gliding isn't as smooth. Then again G3 was doing the same. Not sure why they design them this way. Other than that, it's really good. Also, Goliathus is a soft pad, so that could be the reason, because it's possible it's not perfectly flat or has become waved over time with use.