I was enjoying this for the first three-quarters or so, but then it rapidly got too squicky for my tastes. It starts out as a rumination on preteen/early teenage girl life, with Lizzie and Evie as close as close can be until the latter suddenly goes missing. So far, so similar to The Van Apfel Girls Are Gone (which I only read a few months ago, and did a great telling of this kind of story). However from there, The End of Everything morphs into something more reminiscent of Lolita, with a steadily increasing amount of emphasis on pubescent girls getting inappropriate attention from fully-grown men (not wanting to spoil too much). But see, in Lolita, the whole point of the story is that Humbert Humbert is completely fucking delusional in his belief that Lola has knowingly seduced him. The End of Everything has missed this point, and plays its story straight as one of mutual attraction and seduction.
Now, Megan Abbott's storylines are usually pretty dark and twisted and I certainly wouldn't say enjoying this one means you must be a bad person. It was just too dark for me. However, I do think the blurb did the novel a disservice by not making it clear what the core theme of the novel was. No one sells Lolita as, like, an odd couple fugitive novel, and in being more disturbing this one needs the warning much more! Some people in the comments of other reviews have claimed that if you warn people what the central theme is then that's a “spoiler”, but wtf, people need to be able to make informed decisions about what they read too.
This is not an objectively bad book - indeed, if you don't think your sensibilities will be offended by the major theme then you can expect the reward of a well-written thriller with some real relatability for anyone who's ever been a 12-13 year old girl. But also know that if you are interested in that kind of story, The Van Apfel Girls does a very similar thing without the Lolita element, and I thought it was better.