Ok, I've said this before, and I'll say it again. The trigger is not the best, but it is pretty good. It does suffer from some QA issues, manufacturing issues, and a design issue.
The design issue: The firing pin block should be radiused, and not chamfered. It's get rid of some of the grit.
The manufacturing issues:
1) the trigger bar is stamped steel. It is stamped and bent in a way to keep the smooth finished side of the metal in contact with the sear, but you get the stamped edge in contact with the firing pin stop. The quality of finish on this edge varies GREATLY from gun to gun. About 5 seconds of TLC at the factory would get rid of this issue, but S&W doesn't do it.
2) The gun NEEDS lube on the firing pin block, especially due to 1) above. THe gun also needs some lube in other places. S&W for some reason ships the gun BONE DRY. Put some grease on the firing pin stop that will stay in place, dry fire a bit, and things will improve a fair ammount.
The QA issue:
1) The face of the striker leg that engages the sear can vary. S&W simply needs more QA on this part. I've gotten one that was nice and smooth that looked like it got some TLC, one that was average, and one that had tool chatter marks in it. It got polished at the bottom where the sear engages, but polished chatter marks still feel rough.
I think these are the main reasons that opinions vary so much regarding the trigger on the M&P. Some stores prep a display model by carrying out proper maintenance (i.e. lube it up) and others don't. some stampings have a cleaner edge on the nubbin that engages the FPS than others. Some guns are coming out the door with a half-assed striker.
As far as a great trigger, from the factory, I think the best you are going to get is pretty decent. However, for a striker fired gun, it is the first (IMO anyway) that feels anything like a trigger on gun with a hammer and mainspring. Some folks get a little carried away because of that.