Originally Posted by TheOOB
The CR system was broken, as the number CR didn't actually mean anything, it's just an arbitrary assignment of how tough monster feels. At the core of the d20 system is a lot of math, which the CR system ignores. There's no indication or rules for how much health, AC, or damage a creature should have at different levels, every monster is just placed where they feel right.
If CR meant something, we would have never seen the giant crabs at CR 3
That's largely because 3.x didn't have a robust mathematical "spine" like 4e did, instead relying on its class/level system to try and build monsters in PC-like fashions.
With 4e, I know (for example) that a monster should have (Level +5) attacks vs. AC and do an average of (Level + 8) damage. You can still break the system by doing stuff like giving at-will stuns or whatever, but the math is directly related to creature stats. On the other hand, I could throw a high Strength, Natural Armor, or Con at a 3e monster, have it mess up balance, and leave the CR unaffected.