I liked Beauty very much. As I remember it, Tepper is able to create some truly bizarre and vivid alternate realities. But there are parts of it near the end which might not be entirely palatable to today's SFF fans. At the time I read it, I thought I understood the point she was trying to make in that part of the book, but considering everything she's written since, it would seem not.
I was also impressed by The Awakeners.
Marianne, the Magus, and the Manticore, is a slighter work, but also, I would say, one of her most imaginative. It's just fun to read.
I read Grass so long ago, I don't remember any of the details. I do know that I thought it was good at the time, but I wasn't in love with it.