The MR762 has a forward assist. I don't think there is another AR based 7.62 that has that at the moment. I think that's really the only thing that sets it apart, honestly.
Here is my take on H&K, and for the purposes of full disclosure, I own a lot of their products: roller locking guns, handguns, and even some of their newer offerings like the MR556 and a 416 upper. H&K is in the business of making money.
They make money by making what their customers want. To make more money, they also look at ways to cut their costs while charging lots of money for what they make for less. The first of these two goals led to the the 416/MR556, the 417/MR762; while the second goal led to their polymer guns like the UMP and G36. Of course, producing less expensive products also means you have more room for movement when trying to stay competitive on government bids.
The interesting thing is that I believe that when given the choice between the G36 family and the 416 family, more European end users are choosing the later. I nevertheless think that the next generation of firearms will look more like the ARX-180/G36/ACR/SCAR/CZ 805 BREN platforms. H&K is even trying to spice up the G36 by bringing the controls closer to the trigger guard to make it faster and more ergonomic to reload. Somethings, like the AR platform, die hard though.
So, I guess to go back to my original point, not much sets the MR762 apart from the herd. It's kind of like BMW, then Porsche, and now supposedly Bentley and Aston Martin all making SUVs. There is money on the table, they are going to try to get in on the action. People buy SUVs, so let's make an SUV. I may wind up buying an MR762 at some point, but I don't think it's as revolutionary as the SCAR 17. At least I don't need a bigger garage for my MR762.