Summary: My g400 was dying on me and completely disconnecting both the pointer and my K200 keyboard, so I picked this up as a replacement. After 3 years of having the g400, I wanted something that'd have the same fit, etc.
Pros: -Same ergonomics as the g400, obviously
Cons: -Scroll wheel is rubber-ized rather than a hard-matte material -More resistance to scrolling up/down due to the rubber cover/material's friction, which may not bother some, but I do keybind scroll for things in various games
Summary: I love this mouse. It's a throwback to the very first gaming mouse I'd ever owned when I was 12, and it's a faithful reproduction with just the right amount of improvement. Some gaming mice on the market look as if they have been designed in a laboratory for non-human hands.
Summary: Good mouse, has all kinds of features, but these things are pretty fragile for something that costs $70. I had a G400, which I liked very much, but I accidentally broke the cable. I had another logitech gaming mouse at work, and also liked it.
Summary: I bought mine from a local Radio Shack I used to have a Corsair M65, but I needed a new mouse because it's sensor started flaking out. I spent hours searching for a new mouse with a similar shape, that could fit my claw / fingertip type grip. I didn't find one.
Summary: Bought this mouse primarily because I wanted to have a couple extra buttons available when playing computer games. I did my research, settled on the G400s and have been happy with it for 9 months running now.
Summary: I have had a few mice since my old Logitech MX518 stopped clicking and none could compare. I found this mouse in a store (sorry Newegg) and when I picked it up it felt exactly like the MX518. I'm a fingertip user and this is the best fit I have ever found. Love it.
Summary: The Logitech gaming software is very user friendly and has a nice design.
Pros: -It has enough buttons -Good size -Well placed buttons -Nice paint job -Great for claw gripping
Cons: -Mouse click is very un pleasing -Somewhat un pleasing ergonomics -When I programmed one of the side buttons it didn't seem to save properly. It said it was programmed to "1" but it still is "L". I even let it load for a night but still works as the "L" button.