I can say that mine is incredible but I have dual SSD's on RAID 0 and a much higher end graphics card.
I can speak to the build quality though. ASUS ROG laptops are the highest quality gaming laptops on the market. They are heavy but run cool and are incredibly sturdy. The look of them is really nice and clean, and I love how understated it is.
The keyboard is incredibly comfortable and is the best for gaming I have experienced. The touchpad works fine, although it's a gaming laptop so I usually have my mouse connected.
As far as specifications go, the G750JM will be well capable of playing any game on medium to ultra depending on what it is of course.
It's a great machine.
Thanks for your 2 cents, build quality is very important to me as well, so I'm happy to hear it's well built. How do you find the screen?
And does that little subwoofer work - I read somewhere that the sound is a bit tinny?