I just got mine, too. Pretty much what majnu said.
I suppose I like the option of a free scrolling wheel, but I can't see I'll ever use it. Web browsers seem to only scroll x number of lines at a time anyway, so you don't need the resolution of a free scrolling wheel there. I used it free scrolling in Rift, to zoom in and out, but the fact that the wheel is so easy to scroll means it's not easy to stop it scrolling and move your finger away without catching it and making it scroll a bit in one direction or another.
I don't find it top heavy and don't need a bungee or anything. With my previous mouse (MX510) I had to position the cable 'just so' in order to not have it alter the feel. With the G502's braided cord, I played some games, had the cord just lying pretty much straight back on the desk, and didn't notice it at all.
Maybe you can't remap the scroll wheel using Logitech's software, but I'd probably use X-Mouse Button Control for that.
Thumb buttons 4 and 5 are in a better position than the MX510, making them easier to press.
I find it too easy to press the 'scroll left' mouse button when trying to press middle mouse, but maybe that's just the way my finger is.
It works surprisingly well in Linux, despite the Logitech software not supporting it there. Because of that, if you want to reconfigure it, it'll have to be done in Microsoft's Windows (or a Mac — I didn't check). It can remember the settings on board, so they'll work wherever. For example, I had a game of Xonotic in Linux and was able to use the settings I had configured in Windows to change DPI in-game. However, I couldn't get it to send extra button event signals for the extra three (four if you count the 'change profile' button) button, so those three DPI buttons will have to remain DPI buttons in Linux. In fact, those buttons don't even send any recognisable signals to the OS.
It's only been six hours use but so far I'm happy with it.
Edit: Oh, and it requires a powered USB port, otherwise it won't work. That is, if you're using an unpowered KVM, as I was, it won't work.