I picked up my S&W M&P15 last night. I can add much in the way of "commentary" because I'm still ignorant, although I've been reading the manual they enclosed. It is chambered in 5.56mm and have a 1/9 barrel. It came with a 30-round Mpag magazine (I bought three metal 30-rounders earlier).
(And I just COULDN'T resist!!)