Just my opinion, of course.
- I find it silly.
- It was obviously based on the alignment chart.
- It contains planes designed to fill in the gaps on the alignment chart.
I'm a voracious reader, and this cosmology seemed so shallow and pathetic compared to those I'd read in fantasy literature.
It seems more about game mechanics than flavor. I know that you can create flavor for it, but I never bothered to do so because it felt gamist to me.
It may be related to the fact that I have a strong dislike for "intelligent design" campaign settings where there are gods living in the planar suburbs who created everything from the worlds, to the races, to all magic (including arcane magic).
I have no need for planes where the gods live, since you can never prove that gods exist in my games.
I have no need for planes where souls go when they die, since I prefer a cosmology where souls are reused or recycled via reincarnation.
I have no love for generic D&D lore. I have always (from age 13 when I began running this game back in 1978) preferred to create my own cosmologies and lore.
Even when I ran in Greyhawk, I removed the Great Wheel from my cosmology, and I removed the gods as a tangible force in the world.
I don't have to do any of this with Eberron (which I occasionally run) since the gods are intangible and imperceptible in the setting, and the cosmology is different enough to be interesting.