If you're thinking about buying this series, don't. Reason being it's not the complete series. It may contain 51 episodes but D.Gray-man is over 102 episodes in length.
Why is this a problem? Funimation in America released the DVD set containing up to Episodes 51 over 7 months ago with no signs that they will continue this series(They've released their October release schedule already)
Because of this, the series has been left half finished, you will not get a complete feeling when finishing up this boxset. And with no sign that D.Gray-man will ever be finished, why waste your money?
My advice, hold off until the last 51 episodes get dubbed, if they ever do, otherwise you're throwing your money away.
I realise some people may vote me down on the grounds that this isnt a *Review*, It is, more reviewing the product and the release method.