The G400 is a dark horse in logitech's lineup. After trying a wide variey of mice, some rather expensive, some cheap from logitech, razer and the rest over the years I though I'd do some sensor digging after my G500 bit the dust. It seemed many of the issues I'd been having with mice over the years were down to their sensors. The G400 uses an optical sensor as opposed to IR or laser on high end gaming mice, it's also got a lower dpi range than many sensors too. Don't let this fool you, just like megapixels on cameras, numbers are not everything.
The G400 comes well packaged and comes with logitech's fantastic warranty service should you need to use it. The mouse itself has 2 large feet, a little foot in the middle, right of the sensor. Back and forward buttons, dpi up and down on either side of a well ratcheted scroll wheel that doesn't support left and right tilting nor logitech's super scrolling wheel and lastly a windows switch key that needs software to work. No calculators strapped to the side, no changeable weights, grips or anything else that adds only to the price and complexity.
The mouse works well in either claw or palm grip and is light in the hand. Where this mouses speciality is, is in the optical sensor it uses. It tracks fantastically, instantly in FPS games I realised I was far more accurate with this than I was with any other mouse I'd used. You don't have to counter for angle snapping or drift, it just tracks properly. Another point of note is I have a large sheet of glass as my desk. Most mice either don't track at all or the few that do track are very jerky. This has absolutely no problems at all. However I prefer the comfort of a cloth mousepad.
The software from logitech is capable if a bit bloated. I personally don't like peripheral software and thankfully unlike the mice with hundreds of macro buttons that need software to setup and use you can plug this one in and get into the thick of it without any issues.