In the Ruins is basically a reprise of this position, but no new details are revealed. The good are shown to bee good, the evil confirmed evil, those driving events still shape them, and those with no say are still shaped. I literally can think of only a single spoiler-type event, and while it might be emotional it in no way alters the direction of the plot that I can see.
Unless you are committed enough to the series that you’d rather not pull out, I’d recommend browsing the book before buying. Personally, I’d be happier reading a 200-word summary of this latest book and saving the money for the final one, knowing it was final.