I like my M&P.
About the only things wrong with it from a design design standpoint are some minor control layout issues, and the striker design. I'd file these under teething issues of a new design, and they have mostly been addressed.
If you have long thumbs and a good, high grip, your odds of interfering with the slide release is fairly high. This won't be an issue for most people, and can be fixed with a little practice, or a file.
If you have a low grip and poor recoil control, you can hit the mag release. S&W has attempted to address this by making the mag release stiffer (I think with changed geometry on the mag catch internals rather than changing the spring rate).
THe original striker was an L-shaped deal and would break with dry firing. The current version is a J-shaped unit with relief cuts near the front. I'd still use snap caps for dryfire practice.
Everything else wrong with it has been a matter of quality control.
There were a bad batch of front sights that would move when they shouldn't.
There was a bad batch where the melonite process had too many slides going throguh the bath, and thus you were getting slides treated with a weak solution. The result was it accelerated rusting when it shouldn't.
There was a batch of mag catches that were improperly hardened that would start failing and droppign mags free.
There was a bad batch of 9mm extractors. They seemed to be cut not quite right.
These all seem to have been addressed thoroughly.
However, it seems that whenever S&W gets a large order for something, QC seems to slide. However S&W customer service is good, and they will make it right if you get something that looks like it was made on a monday or a friday.
The vast majority of them work fine and are accurate.
