Here's my 2 cents worth when comparing my m&p 40 to my glock 22:
M&P 40 Positives
1) Better ergonomics than the glock 22.
2) Interchangeable backstraps.
3) Sweetest/Softest recoiling .40 caliber handgun that I have ever shot. Period.
4) So far it has demonstrated pretty good off-hand accuracy out to 25 yards.
5) Better sights that are easier to adjust and are made of steel rather than plastic.
M&P 40 Negatives
1) At this point, the glock has a better out-of-the-box trigger than my m&p 40 (at least imo). According to various internet accounts, the m&p's trigger is supposed to improve with continued use. I have owned my m&p for less than 2 weeks now so I'm currently stuck in the "I'm still waiting to see that" mode in regards to its trigger performance.
Glock 22 Positives
1) As stated the glock has a better standard (5.5#) trigger with a much much much better reset.
2) Glocks tennifer finish is about as durable and time tested as a gun finish can possibly come. Glock tennifer finish = A tough dang gun finish that is able to withstand dang near anything the world's elements can throw at it.
3) Aftermarket support for the glock is enormous. If you can't find a particular accessory for your glock then you simply aren't looking for it all that hard.
4) Glocks reputation as a no-nonsense defense gun is second to none and---in terms of shear reputation---is probably rivaled by the 1911 and ONLY by the 1911.
5) I can shoot my glock 22 slightly more accurately than I can shoot my m&p----at least so far.
Glock 22 Negatives
1) I simply do not like the grip angle of the glocks when I compare them to other guns like the XD's, M&P's and the various 1911's. Glocks don't have an awful grip but, on the same token, they don't have a grip that I would prefer over the other firearms that I just mentioned.
2) Glocks tend to feel rather bulky and blocky to me whereas the m&p tends to feel thinner and better suited for concealed carry.
3) For better or worse, glock 40's tend to have a bad rep when it comes to KB's especially when reloaded ammo is used. This point can be debated all night long but, rightfully or wrongfully, this rep exist for glocks and that's a negative in my book.
4) I don't like the factory 3-dot plastic sights that come on a glock. I realize plastic sights are cheaper to produce but, imo, steel sights are better to use and are (probably) more durable in the long run.
5) Due to the glock 22's grip angle and general ergonomics, it is my opinion that the glocks tend to recoil more than their m&p counterparts. This is especailly true in the .40 caliber variants.
M&P 40/Glock 22 Pushes
1) I like the m&p's steel magazines more so than the glocks plastic magazines. However, as a flip side to this, the m&p mags are twice as expensive as comparable glock 22 mags plus they are a bit harder to find locally. Glock mags are both very abundant and very cheap.
2) Ease of disassembly/assembly: I've owned my m&p for only 2 weeks now so I really don't know how easy or difficult field stripping an m&p would be in comparison to my glock 22. It's probably pretty easy and I know glocks process is easy.