I have very few criticisms of the G-Pen M712, and even those are more like minor nit-picks than serious problems. Compared to the slim and lightweight Wacom pen, the M712's pen is a bit clunky. It contains a AAA-sized battery, and consequently it does feel a bit bulky, especially if you have small hands. Also the pen has no eraser on the back end, and the buttons do feel a bit cheap, but it does come with a couple of spare nibs and a tool for changing them, which is a nice touch.
My other nit-pick is the light that indicates that the device is powered up. It is bright blue (of course; isn't everything?) and flashes on and off in a very distracting manner. It's also completely unnecessary, since the buttons also have indicator lights that come on when the device is operating.I suppose I could just put a bit of black tape over it...
For a remarkably low price the Genius G-Pen M712 offers attractive and efficient design, good build quality, decent performance and a useful range of features. For about 25 percent of the price of a Wacom Intuos3 it offers about 90 percent of the features, and even adds a few unique features of its own, which is pretty spectacular value in my book.