I feel like 3e told me something like:
The DC for walking on ice is X.
Whereas 4e says to me:
Use a balance check to walk on ice. Set the DC depending on how much of a challange you want.
I REALLY like that.
See, to me, if I see "The DC for walking on ice 12", I can say, "OK, this is very slippery ice, so it's DC 18" or "This is ice with sand and gravel in it, let's make it DC 10". It's very easy to go from "what I imagine" to "what the rules need to be to include it in the game". With 4e, it's more like "The party is level X, so I need a DC Y challenge for them. What makes sense for that?" I have to work from number->thing, instead of from thing->number, and maybe it's due to a lack of experience with the system, but I feel I need to do more mental work to get the same result. (For another example, in Hero system, I might start with "I want a really intense fire burst... that's energy damage, obviously, and it should be about 12d6". The 4e way, in contrast, seems to me to be saying "You want a 12d6 energy blast -- now decide what it is."
Does that make sense?
I am used to imagining a world, or a setting, or a scene, or a character, and then turning them into numbers. 4e starts with the numbers. (In 3e, I'd day, "This ogre uses a large axe. An axe does 1d12 and his Strength is 18, so that's 1d12+4 damage." In 4e, you start with "A brute of this level should do 2d10 damage. I guess that could be a large axe." I'm willing to grant that, with practice, this could be just as easy, and possibly even more creativity-inducing, but right now, it's a major hump to crawl over.)
Again I get the opposite reaction. I feel like the great wheel constrained me more then anything I've seen so far, just in the very idea that it's a closed system. Adding stuff to it was patch work at best.
Sheesh, with infinite planes, you could add ANYTHING -- and still use "official" content.

But like I said, the issue isn't "The great wheel is constraining" but "an official, rules-bound cosmology is constraining". 3e took pains to make sure the Great Wheel was one model of many, one of the better innovations. This was a chance for the 4e designers to do something REALLY daring, but instead of doing so, they just replaced one cosmology which only worked for some games with ANOTHER cosmology which only works for some games -- and they did so in a way which was tightly bound to the rules, making it much harder to pry it loose.
4e seemed to want to go towards a system where "rules" and "world" where firmly divided, and now, they're muddying it again. I find it very hard to really figure out what the overarching design goal is. Every time I think I've got a handle on it, they change their minds.
