Like he said, dont expect match grade AR accuracy out of it, but thats not what it was built for.
I shot with some buddies of mine out in the desert, got to see an ACR in action. It was reliable, and reasonably accurate. Between it, a SCAR, an FS2000, 2 AR's, a MSAR Aug clone, a Sig 556, and two Arsenal AK's, it was the third most accurate, behind only the AR15s.
Reliability-wise, it was one of the five guns that was able to go through a whole case of ammunition without malfunction. Those being the ACR, 2 AK's, FS2000, and 556. Oddly enough, the SCAR malf'd twice. The MSAR was a jammomatic, as was one of the two AR's.
I'd like to have one, but I have other rifles that do roughly the same thing, so its sort of low on my list.