I had an M&P 40C briefly before returning to 3rd GEN pistols. I found it to be well designed, easy to strip and insp, and a nice shooting pistol. I preferred the ergonomics to my G-19. I didn't keep it because I liked the design of the all metal 3rd GEN S&Ws better, although it's a bit of a hunt to find what you want. I also own a SIG 229 in 40 S&W and found it a more comfortable pistol to shoot in that caliber. If I were buying another compact M&P today, I would opt for the 9MM.
Frankly, I think the M&P series has out-glocked the Glock in terms of innovation. My two cents worth, anyway....