Whether you play FPS, RTS, or MOBA games, a good mouse is one of the most important tools in your arsenal. Many manufacturers try to lure gamers in with fancy LEDs, custom weight systems, and the like. Logitech chose a different another approach and just created a series of solid gaming mice with a great optical sensors and no additional bells and whistles. One of these mice is Logitech G400, a successor to the well-known MX518.
I had personally been using Logitech MX518 for over 6 years until its mouse wheel finally broke. I didn't have to look very far for a replacement since Logitech released the new G400 right at that time. This peripheral is exactly the same size and shape as the MX518 - a large, ergonomic right-handed shape suited for so-called "palm grip" and, to a lesser degree, "fingertip grip", and has the same button layout as well. You got your standard left, right, and middle mouse buttons, DPI+ and DPI- buttons above and below the wheel, a Tab / Document Flip button, and two side buttons which come in handy both in games and in navigating the internet (bound to Back / Forward by default).
So, if all these things are the same as in MX518, what's new? Logitech still didn't add on-board memory or other fancy (and, I believe, mostly unnecessary) features, but they did upgrade the optical sensor to a new version with higher DPI and no angle snapping. The color scheme is also new, and a little more serious and somber compared to its predecessor - solid gray and black instead of crater images.
To sum up, if you've used MX518 in the past and liked it, you will love the G400 as well. If you're looking for a large, ergonomically-shaped mouse for gaming or everyday usage, G400 will serve you well, too. Its solid form won't look out of place on a designer's or manager's desk, unlike those gaudy gaming mice from other companies.
Logitech G400 and MX518 Side by Side
Another Update: Logitech G400s
Unlike its predecessor, Logitech G400 didn't last very long on the market. It was recently replaced with the new G400s, which still features the same comfortable, ergonomic shape and button layout, but offers some minor improvements in the optical sensor and the microswitches.
The default USB polling rate has also been increased to 1,000 Hz for the lowest possible 1ms response time, which is pretty much par on course when it comes to gaming mice. This new offering from Logitech is certainly aimed at gamers, as evidenced by its fancy design and coloring.
A quick comparison between Logitech G400 and the newer G400s. Frankly, I like the original's appearance better, as the G400s has that exaggerated "gamer" look as opposed to more sedate color scheme of G400.