Some of what she did was very simplified, I think, because of the age group it was targeted at. I have a similar reaction when reading YA and/or MG NOW. I just DO NOT like reading about young relationships and/or school experiences. It leaves me wanting more.
I agree with you about the religious aspect. I thought it was very overt and could have been more seamlessly layered in. She wrote some other books that were much better done. I particularly liked An Acceptable Time, which was focused on an older character and a very different setting. there were some semi-religious themes, but it was more subtle. Medie, you might like that one since it touched on some druidic and celtic practices. I would classify it as YA.
It's funny how we read things as kids, or even watch movies as kids, and don't see certain messages. I am floored by some of the awful things in the older Disney films. They are extremely racist.
I too, didn't like the suburbia thing. It tripped me up even as a kid.
However, I do find some authors preaching their personal views again and again to kind of melt into a background hum. Heinlen, for instance, I just get over. I fuhgedahboutit and read the books for whatever else there is.
L'Engle's religious views are prevalent in most of her books. I didn't like that she explored some of the stuff I thought was least interesting and ignored the things I found most interesting, like Charles Wallace and his intelligence and the odd family dynamics. She NEVER went into this in any of her books. She completely glosses over it, portraying them as this loving family, but never doing more. It struck me as very shallow. All the funky scientific stuff mixed with flimsy fantasy and religious themes fell a little flat when there wasn't as much solidity to the characters as I wanted.
I did find more in some of her other books. There was poignancy in a few relationships and she touched on some interesting things. I liked it, but I definitely would NOT feel the same now about her as I did at 15.