As a GD owner, I'd have to agree with the generic assessment that their quality is a step above many (or most) other manufacturers at a similar price point. This would apply to rig construction itself more than the "systems" within it. The AC unit, fridge, furnace, water heater, stove, pump, etc. are the same as can be found in many other RV's. But the trailer itself has a little better quality finish on the interior, ours has Dexter axles (LCI frame) and good fit/finish throughout.
What they really claim is superior customer service when compared to other manufacturers. Time will tell, but so far I've been pleased. We've had a few very minor issues with ours that we took care of ourselves with minimal effort, but the one thing you can't "repair" is the control board on your water heater. Last trip out, our water heater failed to work. We called GD and they quickly sent us a new control board, claiming that this was the cause of 99% of failures. It took one minute to replace and we're back in business.
Stroll over to the GD Owner's forum and read some of the threads in General Discussion. They have issues just the same as many other campers, but owners appear to be very satisfied.