When talking about 'Red Seas Under Red Skies' I mentioned that it was almost like 2 or 3 novels in one book. 'Republic of Thieves' is also two novels - but rather than being presented sequentially, they're mixed up. One starts where the last book left off, and the other is told in flashbacks to Locke Lamora's youth (and YES, we finally get acquainted with Sabetha!)
Yes, I suppose the flashback sequences do relate to the 'present' action - kind of. But I think I would've enjoyed both stories just as much if not more, if they'd been presented separately - one as a 'prequel.'
Content? Well, I don't want to give anything away. But it fully met all my expectations. Fantasy adventure, lots of derring-do, a good dollop of humor.
It's a must if you've read the first two - but yes, you should read the first two first.