Amy is a really frickin cool character. I'm talking about in the literary sense. One of the things that I disliked about Their Eyes Were Watching God was the Tolkien-esque feel of all the characters. There were the good guys and the bad guys and everything they did and everything they said supported their status as a good person or a bad person.
The book Beloved is much more George RR Martin-esque, as there are characters that I either don't know how to feel about (Beloved) or characters who I both love and am annoyed by at the same time (Amy and Denver).
Amy is a really cool character because she's not the knight in shining armor coming to save Sethe. She sort of stumbles onto Sethe, calls her a "nigger woman" or something like that, and keeps rambling on about her pipe dream of buying velvet in Boston (.... okay?). But the more I read her story the more I liked her.
She made it seem like she really didn't want to help Sethe and wanted to move on towards Boston, but as readers we were kind of made to feel that deep down she really did want to help Sethe. When he eventually sticks with Sethe for a few days and saves her from frostbite, our hopes are confirmed.
All in all Amy is a really well written and interesting character. She's written as if a bunch of strings were pulling her in all different directions.