I'm with the negative side on this - I didn't think this was a terrible story, I just think it was overwrought, and unbalanced. The hook - a global crisis from the perspective of someone who is more caught up in their personal affairs - was interesting, but, as others have pointed out on the thread, the story ended up feeling more like two stories (Jenny's relationship problems + aliens) meshed together, not like one story with two strands.
On the less evaluative and more practical side of criticsm, I'm a bit confused about the alien's plan, killing 90% of humanity is not going to make a major change. There are currently about 6.75 billion people on the Earth. 10% of that is 675 million, which was the population of the Earth in the early 18th century. And, with modern technology and medicine (presumably, enough doctors survived in small towns, non-Urban campuses, and in countries like Finland, Israel, and New Zealand, that are highly developed technologically but have no cities large enough to have vanished before the culling was done), the population will increase much faster than it did for most of those 250 years. Probably, the Earth will return to current population levels within 100-150 years at most. Were the aliens going to repeat the exercise?
Actually, mentioning Israel - how did the Aliens determine city population? If they went by official city boundaries and people counts, Tel Aviv, a city of less than 400,000 people, will almost certainly be spared. But the boundaries of Tel Aviv are mostly a technicality and have no pratical significance other than tax purposes and parking permits, as it is really just the central city in the continuous urban sprawl of Gush Dan, which contains 2-3 million people, depending on how exactly you count its boundaries, and would thus be larger than Rochester and included. I wonder what criteria the Aliens used - would suburbs count for city population sizes only if they are officially incorporated?
(I originally had an additional rant on how inappropriate the term "mass genocide" is, both in general and in the context of this story. I think using it here - apparently as a way to say "really really massive homicide" is highly problematic, on many levels, and offensive to victims of actual genocide - the distinction between genocide and homicide is not the amount of people killed, but the motivation and goal of the murderers, and it is worth keeping that in mind. But I decided to leave out the ranting, and just make note on this poor choice of words).