I own two of the newer model S&W revolvers, and also a few of the older models.
My 625-8 45ACP is well finished, the action is smooth, and is really accurate with just about any ammo I have used in it. I did install a C&S long firing pin, and lighten the action. I am well satisfied with it, having owned it for at least three years now.
I also have a 629-6 44 mag classic that I bought used, made the same modifications as the 625, and it is also very accurate and performs well. Sometimes I think it is a little muzzle heavy, with it's 6 1/2" full lug barrel, but it does help with recoil.
Both guns still have the lock system intact, and I have had no problems with it so far, but I also do not use the lock.
In a lot of ways, with the use of the modern CNC machines, and the MIM parts, the new revolvers are smoother and more tightly fitted than the old guns. I know this will cause a lot of heartburn for the guys who love the old guns, but I have owned a vary of S&W revolvers over the last 35 years, and that is my view on the guns.