I have to ask, how much did you pay for MB-D15? The pricess I see online are $250 for MB-D10 and $269 for MB-D15. I did not have a chance to compare the grips for D90, but I did not think that the quality of the genuine grip matched the price and my expectations. For $250 I would want the grip to feel as if it was made a part of the camera. You are saying it is not quite the case. Then I just don't see what justifies this price. For comparison, this is more than a superb 35mm or 50mm 1.8G prime lens.
I think I will wait for the third party grips to come out to hear what people have to say about them.