I pretty much completely agree with your list here are my personal favorite ages:
I like Riven so much because of its size, its distinctive style, its haunting isolation, and its attention to detail. Exploring it is amazing, with so many amazing visuals and important objects. Everything in the age, from the architecture to the ocean and the Black Moiety knives, has an almost creepy, tribal style. They give a certain mood, of a strange world that is both literally and figuratively being torn apart. The music echoes this, a haunting, watching, tribal sound that makes you feel like someone is just waiting for you to make a mistake... there are subtle things you don't notice, like the importance of the number five, or the sacrificial whark contraption and the toy in the schoolhouse that shows how ingrained this ritual is into the inhabitants of Riven. The things on Gehn's desk are so fun to look at, showing the strange water and many other studies of Gehn. Everything about Riven has a certain feel, and is probably the most immersive age in the entire series.
- 223'd Age (I think thats what its called)
This age is so visually amazing, with its dramatic lighting and strange double-mountains. There isn't much to know about the age, other than its windy, (and if you do know about the age, I'd love to hear about it!) but it seems to capture the essence of the game (Riven).
Haven is just amazing, with such a rich atmosphere. The broken, wind-torn ship, embedded upright in the ground, surrounded by constant gusts of sand and dust, and lined by fang-like rocks that signify the harsh nature of the age as massive waves crash in the distant... it's just beautiful. But it also has a harsh brutish nature that seems to say, "kill and eat, or be killed and eaten." The only complaint I have about Haven is Achnear. He just seems so... calm, sane, and rational, the opposite of the Achnear I know from Myst. He didn't even laugh once, as far as I can remember!
Spire is just so cool, for many reasons. It's one of the most amazing looking ages of any game in my opinion, and has awesome science. The contraptions of Sirius's desk are great (almost as good as the things on Gehn's desk), and the devices he has are just cool. The entire age almost describes Sirius's true identity, dark, calculating, scientific.
Narayan is (as the OP said) possibly one of the most creative age of all the games. The visuals of the age are so unique, with its lattice trees above the clouded ocean. By the way, my favorite part was when Saavedro smiled creepily and twirled his hammer around
There are other ages I love, of course, but this list is pretty long already... so anyways, those are some of my favorites.