Part of being a Smith & Wesson fan is pissing and moaning and throwing a temper tantrum every time the company changes anything about their revolvers. It doesn't matter whether the change had any real effect or not, it's always a sure sign that the bean-counters are in charge and the company is going down the crapper and I'm never buying another gun from them and furthermore I'm going to hold my breath until I turn blue see if I don't!
Presented for your consideration:
The Fifth Screw: Well, it didn't really do anything. A five-screw sideplate is a little easier to re-install than later ones, but apparently not all that much.
The Fourth Screw: This one actually did something. The cylinder stop bolt in modern Smiths goes in with a bunch of poking and tweaking at a tiny spring. On older ones you just dropped the bolt in and then inserted the spring and plunger through the hole in front of the trigger guard. then stuck the screw in the hole. No muss, no fuss. Of course, this only matters if you're taking the gun apart and putting it back together yourself.
The Recessed (countersunk) Charge Holes in the cylinder: They only did it in magnum revolvers anyway. No real loss.
The Pinned Barrel: Here's one that can start arguments. With the pinned barrel, you'd screw it in until the hole lined up, and then drive the barrel pin in. This worked fine provided that it hadn't been an off day and the threads were cut to spec. If the threads weren't cut to spec, the force of firing could bugger them all up over time. The barrels after '82 were crush-fit snugly which lessened the chances of this, but...
The Two-Piece Barrel: With the crush-fit barrel, it was torqued 'til tight. Sometimes, this resulted in the front sight not being, you know, straight. The two-piece barrel eliminates this by mounting the front sight on the sleeve, which is always straight, no matter how the actual barrel is tightened. Of course, the inner portion is still crush fit, which can cause distortion of the rifling, something that didn't happen with the pinned barrels... All three methods have faults; you pays your money and you takes your chances. However it's funny to hear people claim that Smith went to two-piece barrels because they're "cheaper". These people obviously can't count machining steps.
Metal Injection Molded Lockwork: Meh. It seems to work fine, but it sure does make it harder to get a nice trigger pull. It does get rid of the hammer-mounted firing pin, which is marginally more breakage-prone than the frame-mounted variety. The MIM triggers, with their hollow backs, look cheap, too.
The Lock: Lots of people have locks on their guns: Bersa, Walther, Ruger, Taurus, HK, Springfield Armory... But none of these people sell tradition like S&W does; it's gone over like New Coke or water-cooling on a Harley. It doesn't help that the lock is visually obtrusive and mechanically suspect, especially on the hard-recoiling flyweight revolvers that make up such a large part of S&W's lineup these days.
Anyhow, this ties into another thought I've had on the subject, concerning Smith & Wesson's new "Classic" lineup. More on that later.