I think it's funny that the VGA thread was flooded with "this has to be next-gen"/"this is next gen for sure!" throughout the trailer when it initially debuted, and then quickly turned and said there's no way in hell that it is.
The reason it doesn't look as good as Ground Zeroes is most likely due to the lighting and weather effects found in that trailer. You're game is pretty much naked, so to speak, in that completely clean, bright hospital setting that the Phantom Pain trailer mainly takes part in. The Ground Zeroes trailer had a nice dark outside environment with harsher floodlights that washed things out, not to mention some killer weather effects to boot.