I'm definitely liking the D&D cosmology as described in 4e. The whole "Great Wheel" setup never really did it for me, as it just seemed like a very artificial construction to cram beings from a couple dozen real-world and fictional mythologies into a defined number of alignment-based realms. It was weird, and I never really cared much for it.
The inner planes, as described with the positive and negative energy planes, para-elemental planes, and quasi-elemental planes also really started to drift into territory that I found unappealing.
But I came to 1e AD&D after playing BECMI D&D for a couple of years. BECMI D&D's cosmology consisted of the prime material plane, the four elemental planes as the "inner" planes connected by the ethereal plane, and the astral plane which contained gateways to an infinite number of outer planes that had no connection to game mechanics such as alignment. Hmm, that last part sounds a lot like the Astral Sea, doesn't it? I've said it a few times, but one thing that really appeals to me about 4e is how it captures a lot of the feel of the BECMI game that I first started playing with.
I love the idea of the Shadowfell and the Feywild as the "darker" and "lighter" echoes of the mortal world. The ethereal plane of previous editions was similarly co-existent with the prime material, but I love the flavour of these two 4e "inner planes." These planes become a lot more accessible and usable as adventure settings when they have such close ties to the prime material and adventurers can find themselves wandering into an echo of the world if they aren't careful. I love the idea of the twilight Eladrin cities existing in the Feywild but crossing over into the "normal" realm at thematically appropriate times.
I actually quite like the Elemental Chaos as well. Planes composed almost entirely of fire, earth, air, or water were always extremely dull, in my opinion. A chaotic realm where the primordial stuff that makes up the world churns endlessly is much more cool and flavourful, in my opinion. And makes for a better place to adventure than "the plane where you spontaneously combust when you enter without the proper spell," "the plane where you appear in the middle of solid rock and suffocate unless you can find an Air pocket," and "the plane where you instantly drown unless you can find an Air pocket." "The plane where you fall infinitely until you hit something at terminal velocity" was slightly more adventure-friendly, but still had a lot of limitations.
I liked it when the 3e Forgotten Realms book dumped the Great Wheel for its own outer-planar cosmology, and I loved how Eberron invented its own cosmology that was completely separate from any of the other settings.
The 4e cosmology just seems so much more useful (in terms of actually using them in adventures) than the stuffy, rigid setup of 1e and early 2e. Planescape made the planes much more accessible in later 2e, and I did like the setting. But as others have mentioned, it was better as a primary campaign setting than as a default cosmology that connected all worlds.