Jews vs Zombies is the easier concept to grasp (there are fewer varieties of zombie than of alien). It struck me on reading the stories that both Jewish historical experience and zombie stories tend to converge on urban environments. There's an obvious part-way cross-over with the golem, which one or two of the writers explicitly invoke. The one that particularly grabbed me was the final story, Adam Roberts' "Zayinim", about a young girl fighting off zombies while thinking about philosophy.
In the foreword to Jews vs Aliens, Lavie Tidhar points out that "The alien in science fiction, it is often said, stands in for the Other in all its myriad forms... To [John W.] Campbell, of course, the Jews were the aliens – but what happens when the roles are reversed?" Another theme that came through to me here more than in the other book was the military tradition of aggressive defence; Roseanne Rabinovitz's story "The Matter of Meroz" combines the two very effectively.
I approached these with some trepidation, as the last time I read a themed anthology of Jewish sf I was unimpressed. There are one or two awful or incomprehensible stories in each of these anthologies, but in general they are very much worth reading.