Well, I just bought its sibling, the 327 TRR8. About the only difference is that the M&P R8 has a different barrel shroud with the lower rail integral, instead of removable.
I haven't had a chance to take it out to the range yet, but it fits the hand incredibly well, and 8 shots of .38 or .357 is a nice amount of 'whuppin' to have in a sidearm.
From what I've seen, folks are pretty divided on the R8 and TRR8. They either lust after it with the passion of a thousand suns or they recoil in pure horror. I was in the first group, which was why mine followed me home last Friday.
If you want what it has to offer (lightweight Sc/Al frame, 8 shots, rails), then it is a fine gun. If you'd prefer a more traditional gun, then the PC 627 or the newly announced Pro series 627 or even the new regular production 627 might be better choices. I just got tired of that thing haunting my dreams.