The Assassin and the Desert was marginally better than the first prequel in the Throne of Glass series but not by much. The writing in this one was improved but still very problematic. The dialogue was cheesy and much too modern to fit with the renaissance-like fantasy world that Maas has created. There were also some glaring grammatical issues. Although the story is written in past tense, there were several awkwardly placed sentences that veered into present tense.
Characterization was still very much an issue in this novella. Celaana is not believable as an assassin let alone the world's most deadly assassin. She only kills one person in this story (which is one more than in the last) despite being caught in the middle of a siege. I will say that I found her slightly more likable by the end of this installment than I did at the beginning. She does show some character development but her arrogance, brattiness, and superficiality still makes her unlikable.
The story could also stand to be tightened a lot. The plot meanders quite a bit and there were a lot of side stories, such as a useless romance, that were extraneous. Overall, I was not impressed, although the improvement in writing and the character development made it a slightly more enjoyable read than the first.