I concur completely with Scott Morrison. Whilst not so knowledgeable as he, I love the Scarlatti sonatas and have recordings by half a dozen artists. Zarafiants is a new name to me, but I am so impressed that I found Scott's review whilst looking for more on Amazon. In fact, I'm disappointed to read from him that there are not 5 more volumes from Zarafiants!
The slow pieces are beautifully expressive, dreamy and languorous. The fast ones are taken at less than break-neck speed, and as a result remain expressive and the playing is incredibly precise and clear.