Q u o t e: I do not like the Diablo 2 attack rating system because I never have a feel for what it really means.
A valid concern, I never really knew what kind of effect it had until I visited websites with the specifics and all kinds of spreadsheets for the various monstertypes.
Q u o t e: I'd rather D3 develop a multiplicatively stacking resistance system that incorporated varying penetration abilities on bosses and a difficulty-based overall penalty.
And that's where you lose me, how are you supposed to know what resistance really means if all kinds of special mobs have ways of reducing it? Do you expect to see their penetration on your UI? Fat chance, so you have the same situation again where you need to visit websites to figure out the real value.
A rating based system with a final % in your char sheet that reliably works against all damage of that type against a monster of your own level is a very clear system. Sure it will not 100% catch boss damage as those will probably have a higher level, but it's somewhat intuitive that bosses can get past your resistance a bit as long as the difference is not too big, most people would probably never notice that the boss is doing 46% damage to them instead of the expected 43%.
The big problem with % ratings and difficulty and boss based penalties is that it screws up item progression.
You have the obvious case of the low level resistance item keeping it's usefulness past it's point, resulting in weird looking sets and panic stashing all resistance items, but imo a much better example is this:
Say you have -100% resistance in hell and maximum resistance is 75% (95% would make the numbers even more crazy), player 1 puts a high priority on resistance and gets 175%, player 2 cares about resistance too, but he likes to wear damage items and doesn't really understand the way resistance works correctly, so he gets 125%.
125/175 = 5/7, so player 2 has 5/7 as much resistance as player 1, but he reduces damage only to 75% instead of 25%, so he takes three times as much damage.
In a rating based world, (without multiplicative reduction) player 1 still has 75% resistance, but player 2 is now up to ~54% resistance, so he takes 46% damage instead of the previous 75%.
In both scenarios, resistance becomes more valuable the more you have, but in the first setting, resistance has to be cheap enough so you can even get 175% in the first place, so resistance reaches ridiculously overpowered levels once you have enough of it and you really can't completely ignore it as -100% will result in oneshot glory.
If we add multiplicative scaling then we get even better numbers with every point of rating resulting in the same amount of reduction.
You could argue that it's cool that players knowing more about the game can make the better choices, but it's bad design to add unintuitive choices that have a huge impact on gameplay, the better player will make the better decisions anyway.
Q u o t e: (*Note: I have a MS in Math so I've earned the right to abuse the equals sign.)
Actually I'd expect math MSc's to be more accurate than your average number juggling highschool wannabe math nerd. The math guys I know tend to make huge jumps in their conclusions that I need several steps for, but they are always 100% accurate.