You know, reviewing multi-volume manga sets can be tricky business - it's not like novels where each book has a distinct plot (or lack thereof), and you can review it on it's own merits. Manga series are one long story or series of stories that don't usually pay much attention to where the front and back cover of a particular volume are. Sure, the covers occur at natural scene breaks, but it's not like once you've read an entire series you can look back and pick out what happened in which volume, unless you're some kind of otaku nutter. If you are an otaku nut-job, you've probably just taken that as a compliment. Anyway, the reason manga series don't have individual plots in individual volumes most of the time is because the original manga was serialized in a magazine, ten or twenty pages at a time, and the mango volumes we get here in the west are collections of those serialized chapters. So it's hard for me to remember where FLCL vol. 2 started. I can remember how it ends - the series has only two volumes in it, which makes it a lot easier to distinguish between the two volumes.
Anyway, volume two continues the saga that started in volume one, and more (or less) is learned about the characters as our protagonist, a pre-teen boy who's in love/hate with his dad's girlfriend/housekeeper who's also an alien that rides a Vespa struggles to contain the bizarre things that keep popping out of his head and going on rampages around the city. And then it ends, and it's quite lovely.
The whole series for me is a completely random symbolic coming-of-age story that expresses with near perfection the horrors of growing up, falling in love with your older brother's girlfriend, every girl you know, and any older woman that smiles at you.