One of the current greats in Hard ScienceFiction. A much better writer than StephenBaxter and at least as good in her chosen field (biology) as he is in his (physics).
http://davidmswitzer.com/slonczewski/
I'd say she's on par with StephenBaxter; both have written dreadful books or stories (e.g., Slonczewski's The Children Star).
What are you talking about? Baxter's best book isn't even on par with The Children Star. Slonczewski knows about characterization, plot, prose and so on and so forth. Baxter knows nothing.