New Nikonian - appreciate and enjoy the abundance of information found here!
I have OEM grips for both a D7000 and D7100 (No need to discuss why a D7000 & D7100 - is what it is) and am quite pleased. Extra battery life, higher fps, and giving more oomph to an otherwise light body. Neither can fully equate with the robust feel of a D2x though; provides nice balance for a 80-200mm f/2.8 which stays mounted on one, normally a 17-55mm on the other.
Can't speak to 3rd party grips, been burned more than once so I decided to pay the price up front.