Again, I am not familiar with editions before 3rd, but the whole CR/Encounter Level system of 3E for me was genius - a system that allowed me to gauge how hard an encounter will be for my PCs? I hadn't seen that before, nor I have seen something after. 4E is clearly a refinement of that prinicple. It is probably also an ultimate expression of "gamist" concepts in D&D, only existing to facilitate the "kill people and take their stuff" trope, but, well, I think it is a very powerful and important tool for DMs. Expanding the system to handle "skill challenge" and quests just seems logical.
The problem with 3E and the entire CR/EL system is that it was easy to break. It was fairly effective at low levels, but very ineffective at high levels. It was like 3E was tested to about level 10, but wasn't tested much past level 10.
Let me give you a few examples:
1. A Beholder: In concept a beholder is supposed to be a single tough encounter for a group of four level 13 characters. In play a beholder dies in roughly a round or two unless the DM was very careful in what magic items he handed out or how the characters were built.
A lvl 13 fighter backed up by a fly spell from a wizard could annhilate a beholder.If the beholder used his anti-magic eye to keep the fighter from getting to him, he couldn't use his own powers on the fighter or party standing in the anti-magic ray.
Then if you had a well-built archer in the group he could practically kill the beholder by himself in a round or two with moderate protection from the cleric. Once again the beholder's antimagic ray could stop the magic, but at the same time rendered his own power inert.
Now that makes a fight against this epic level aberration that is supposed to be a fearsome monster of legend a joke. His own antimagic ray eye has to be used to prevent the party's magic from making him easy to kill, but his own antimagic ray eye also renders his own powers useless. He doesn't have enough AC and hit points to stand toe to toe once engaged.
This won't happen in 4th Edition unless that beholder is designed to be a fairly weak kill. I find that monster design philosophy better illustrates a battle against groups of creatures or epic creatures.
I don't have to design an NPC that has a huge spell list anymore just to match the wizard and cleric. I don't have to stack a ton of magic items on my evil NPCs just to keep up with the fighters AC. I don't have to have the cleric carry around wands of healing just to keep the encounters progressing. I don't have to worry about creatures being one-shotted to a crit if I design them to be an epic encounter that requires everything the players have to win.
Alot more thought was put into encounter design and challenge. It may have started with 3E. But 4th edition did a much, much better job of creating challenging encounters without the oddiity of requiring magic item inflation on the part of both the monsters and the players. I find that refreshing.
Everything in 4E seems to scale better.