Smith and Wesson's new "two piece" barrel is more akin to the two piece barrel on the old Dan Wesson revolvers (maybe the new Dan Wesson's too for all I know). There is a barrel, then a sleeve that slips over it, and a nut at the muzzle to secure everything in place. In theory, the two piece barrel is supposed to be more accurate, at least that's what Dan Wesson fans tell us. I can't shoot near well enough to tell.
I happen to have one of the "classic" Model 19's. It's the first "brand new" Smith & Wesson I've owned in forty years I guess. Now, I'm not smart enough, nor do I shoot enough to tell you if it's "better" than the old ones or not, but it's a darn fine gun. The blue is different, but it's still a nice blue. The stocks are really nice. The trigger out of the box was, well, IMHO very good. I did run fifty rounds of full power 357 factory loads through it and it shot as well, maybe better than I can normally shoot anything.
Yes, it's got the lock and MIM parts. No big deal to me, but if it is to you, I'm not going to try to change your mind.
The new gun has some improvements. The flat spot at the forcing cone has been eliminated. That flat spot is supposed to be the weak spot that causes forcing cone cracking. Now it's a full diameter FC. Also the front lock is now a ball detente on the front lug that should be stronger than the one of the front of the ejector rod.
The pictures don't show it well, but it's that little silver thing just below the barrel (the picture also shows the "no flat" barrel).
It's spring loaded so when you close the cylinder, it pops into place and fits into the machined slot on the crane shown in this picture (just ahead of the cylinder).
I love the "old guns" but I won't hesitate to buy a "new" one if I want it.
Oh, price. The price was less than I'd expect to pay for a NOS, unfired Model 19, with box and papers. More than I would have expected to pay for a run of the mill Model 19 on the used market.