Jessica is a little psychopath. I figure the wavelength of Jessica's mood is about two pages, on average. It's impressive. Anyway, nothing terribly unexpected happens. It's pretty much a soap opera. Very quick to read, I guess, but that's probably its only virtue.
Some of the reviews I've seen indicate that this may not be a totally good example of the quality of the series, though that may be partly due to people reading this after many years, and the whole thing doesn't measure up. Well, I might give the other books a try.
"Oh, Lizzie, do you believe how absolutely horrendous I look today!" -- p. 1
"The idea that he would prefer Elizabeth to her infuriated Jessica, though she was extra careful to conceal this from him." -- p. 4
"The twins squealed with delight." -- p. 14
"Jessica's anguished wail filled the entire kitchen of the Wakefield's split-level home." -- p.14, three paragraphs later
"...[Jessica] was out of the car in a flash, slamming the door so hard that Elizabeth winced." -- p. 18
"'I've decided to forgive you', she announed, beaming." -- p. 19
("Surprised, but not unaccustomed to Jessica's swift changes of mood, Elizabeth...") -- p. 19
"'What about me?' Jessica hissed. 'Why haven't they called my name?'" -- p. 26
"Jessica was ecstatic." -- p. 27
"...Jessica whirled in, smiling as only she could when her day had been a perfect dream." -- p. 33
"Her eyes sparkled with unshed tears." -- p. 37