The problem with 3.x (Outside of the CoDzilla, which is Core Book, the escalation of hit points until Save or Die effects are mandatory, and the Christmas Tree magical item progression) was that you could, quite easily make a character that could be a problem. More often to the GM. Who, if they were like me, were too nice to have make something else.
You know the less than useful type of character that if you threw an equal level challenge at would fold faster than Superman on laundry day, while the other Players would breeze through. That was HELL on my adventure design. Trying to think of something that would challenge the party without crushing two thirds of it, because one character accidentally was superiour than the rest. Hell, with the right spells he WAS the party.
And having run several games/campaigns of 3.x over it's entire lifespan, I can tell you, that as a DM, having to deal with that, every freakin' campaign was not fun.
At least in 4e, it's tighter, and harder, to make it so the GM has to work that hard. One thing I will give praise on 4e is that DM'ing the crunchy bits is easy. I don't have to worry about PC spells, it's all detailed and up to them to take care of, all I need to do is if it's a combat scenario, add the right monsters and watch things explode. Or if it's a trap manipulation, get skill challenges up and running. Otherwise it's RP time with the rare dice roll.
