The Great Wheel worked finely for Planescape, which took the alignment-based arrangement and cosmic symmetry, and ran with it (more successfully in some places than in others - can anyone say anything interesting about Bytopia, for example?).
However, just as Planescape in my opinion suffered, if you used it merely as a "transitional setting" for plane-hopping primes, I think forcing the Great Wheel on general settings also hurt them. Not all things will go with each other, and no matter how nice fine, dark chocolate (PS) is, it's going to suck if you're putting it into your stew (your own setting).
I'm quite happy with the 4e cosmology, overall. Shadowfell and Feywild, in particular, are excellent additions - a faerie world and a dark underworld of ghosts, both close to our world but not quite part of it - are tremendously popular in myths.
As for making the planes more accessible to characters robbing them of their distinctiveness and splendor... nah. In my experience, the inhospitable planes like Plane of Fire were either places where you didn't go (because you would die), until you had the spells / magic items to deal with the local conditions... at which point the place being made of fire became scene-setting only.
Furthermore, I don't see why you can't perfectly well have very dangerous and inhospitable planes in the 4e cosmology, if you want them. The astral dominion of an evil god, where his will is the natural law, filled with his minions and creations? Dangerous as all Nine Hells.
So no, 4e default cosmology isn't Great Wheel or Planescape, and as a PS fan, I think that's a great thing.