Just finished Heist Society -- awesome read!
I was actually really disappointed with Heist Society. For two reasons: 1) the voice didn't seem as fresh or unique as the Gallagher Girl series, and 2) the author didn't seem to have much knowledge regarding Nazi-looted art. Now, that's just my own bias, probably, since it's a subject I care a great deal about, and I've spent many hours in museums checking provenance records.
However, Carter is certainly a great plotter. I'll give her that. And I do love the GG series.