What should be changes IMHO? (I'm a range plinker, a really good one but one nevertheless)
The 300 rnd break in needs to go if it hasn't already. That does not make much sense to me on a service-type rifle.
The ejector should be redesigned, though this may have been done on the newer ones. I know there was a fair bit of dialog about it circa 2007. I can't tell you the number of times that thing came loose until we found a home solution.
The trigger should be polished prior to leaving the factory. The ones that I saw had unreliable functioning out of the box until they had been polished. I can see heavy, or ratchety, or unpredictable triggers, but some of the ones I have seen would not even reset out of the box.
The firing pin holes should be QA'd. For a long time, craters/punched primers were fairly common on the XCR. Not sure if they still are.
The upper/lower release lever should lock.
There are an equal number of design pluses that I would like to see on other platforms, but many of these should be caught before the rifle leaves the factory.
I believe these issues, as well as the handling of the user feedback by the manufacturer has led to some of the "haters". To me, they all seem to be fairly simple QA stage fixes at Robarm, especially given that so many of them have home solutions that the manufacturer recommends.
Once all of the required home solutions are done to a given rifle, they seem to work like a tank, but I wonder why the home solutions were not manufacturer solutions.
Bear in mind that my experience with the XCR ended in about mid 08. They may have changed some/all of the above since then.