The buttons and layout of the mouse leave a bit of room for improvement. The side buttons are a little too hard to push, so it's hard to push them without moving your mouse sideways a bit. This can be a pretty big hassle, especially if you bind these buttons to functions like quick switch and try to use them in game. Also, the dpi switching buttons and far side buttons (those across from your thumb, whichever side you choose that to be) are practically unusable. Unless you hold your hand very low on the mouse (making the scroll wheel and the thumb buttons inaccessible), it's a pretty far reach for any of those buttons making it impractical to use them in “on-the-fly” situations. These layout issues could have been solved if Razer chose to make this mouse a “righty” mouse, and weight it to one side. That would give them a little more leeway given the extra curvature. This design choice doesn't appear to have many drawbacks either because most lefties don't even use the mouse with their left hand, on the left side of the keyboard.
Though the buttons are a little hard to push, there is a lot of room for creativity with their assignment features. From macros to media functions, there are a lot more options for button functions on this mouse than any other I have ever experienced. This just goes to show how good of a job Razer did on the Lachesis drivers. They are wonderfully lightweight and non-intrusive, but don't leave anything out.
As far as the actual performance of the mouse is concerned, the Lachesis is quite a champ. I have heard horror stories in all sorts of places about this mouse and all sorts of problems with its sensor, but beyond the little bit of sticking I experienced, the Lachesis was the most accurate mouse I have ever used. Going into this review, I was pretty skeptical about how practical a 4000dpi sensor could be, especially because I was so pleased with the 2000dpi sensor on the Logitech G7, but I was pleasantly surprised by the increase accuracy and control. Part of this great performance was due to the included feet on the Lachesis, which made for almost frictionless moving. This means that minor adjustments (for example, aiming with a sniper rifle) are easier to make without jumping to far.
On the whole, I am very happy with the Razer Lachesis mouse. Though it suffers from a few layout flaws, the Lachesis is the best performing gaming mouse I have used to date, and I am happy to award it with the OCIA.net Seal of Approval.