I probably can't review this mouse without being bias, as the internet's most eloquent inhabitants would put it. It's the mouse I judge all other mice against, remastered for 2011. Like if George Lucas released the original trilogy, unaltered, but in retina-jarring 1080p.
I've slaughtered nations of prancing polygon people with the original MX518. Using the G400 is like picking up my favorite gun again after being separated it from it a very long time—think Nicholas Cage and his twin gold pistols in Face/Off. The G400 is a few frills affair, a tool. There are not 6,000 buttons. There are no glowing lights. Just a pair of optimally placed thumb buttons, a solid scroll wheel, and quick access dots to quickly jump from less sensitive DPI settings to more sensitive. The ergonomics are perfectly balanced—the contorted bean shape is ultra-comfortable, but not forceful in positioning your hand in a particular way, like some aggro-ergonomic mice. Logitech's macro software is quite swizzy. Cheap for a gaming mouse.
This is perhaps blasphemy, but the truth is, I don't think anybody can credibly claim anymore to perceive any kind of lag differential between modern wired and wireless gaming mice. Wireless is good now, with polling frequencies that match wired mice. So I wish the 2011 update was a wireless model. Otherwise I'd prefer a braided cable, 'cause it'd feel much sturdier than skinny string connecting the G400 to your computer. No official Mac software support is a mild but not unexpected bummer.
Relatively simple calculus is involved here: Do you want a gaming mouse? Do you want it to be (relatively) cheap? Do you want it to be excellent? Done. Buy this. [Logitech]