I am going to talk about both books at once, because that's what makes sense. In recommending these to anyone, I will treat them as one book, one story.
According to Wikipedia, Butler had intended to write a third volume called Parable of the trickster. It would have been great if she did; I enjoy Butler's books very much. (Having read these two, though, I can't imagine the state of my emotional health after a third Earthseed book.)
About Parable of the sower: We enter a civilization - well, American civilization - breaking down; the apocalypse is now. (The "oops, the world broke"-thing has been a clear favourite of mine since Womack's Random acts of senseless violence, which was, therefore, one of the first associations I made in reading this.) You know, when life as you know it just crumbles to bits, it very likely doesn't happen in the blink of an eye. Disaster strikes fast, but some tragedy takes time, years, and probably doesn't exactly catch you by surprise - denial, maybe, but not really surprise.
Lauren Olamina, the young protagonist, is very much aware of where things are headed. Her intelligent observations are refreshing, and I instantly root for her. If a character is charismatic enough, she can carry a whole book on her own. (At times she's unreal; it's hard to match her words to her supposed age, but in unusual circumstances, a lot of unusuals are easier to accept.) She's a preacher's daughter, but she does not share her father's faith. To the contrary, she is devoted to uncovering a different set of truths. The story is told through Lauren's diary, which allows her voice to stay focused and calm, while keeping the sense of urgency, through gaps between dates and other details. Parable of the sower is merciless, but the ending doesn't prepare me for the next book at all.
The parable of the talents took me a lot more time to get through - because parts of it are simply very unpleasant, in the intentional and story-relevant way. Butler has made me care enough about these characters to make it quite painful to go through this bleak, bleak piece of the near-future with them. It's good - actually that's very good, but also impossible for me to read several hundred pages of in a single sitting. Butler tells the story of a world that has already gone to pieces; then she has the broken remains of the people trying to go back in time, panicky; A religious leader becomes president. The slaves vote for him, too. More and more women's tongues are cut out. Olamina keeps hers, but her losses are many.
I wouldn't read this if I was feeling especially thin-skinned. If the measurement of an author's skill was solely how much her stories and characters could affect me, I believe Octavia E. Butler's profile would be embedded on the gold medal.