Starting with what will likely be a mostly-copy and paste Codex (which comes in Standard Neophyte, Patriarch Collector's Edition and the horrendously expensive Get Of Her You Bitch Limited Edition) we then get a selection of characters for all occasions; Nexos (probably the pick of the bunch for us), the venerated Magus (who comes with an alternative hand), Clamavus (who comes with an alternative head), Sanctus (who comes with an alternative weapon), and Locus (who comes with an alternative head). There's also Jackal Alphus, the leader of the Atalan Jackals, a very cool set of mounted skirmishers for a rather good price! There's also a new terrain piece that's actually more a weapon than a terrain piece, the Tectonic Fragdrill and the repackaging of the Brood Brothers - Cadians with a Genestealer Cults Upgrade Frame.
There are of course Genestealer Cults Datacards and some rather odd Genestealer Cults Dice.
For those into added extras, if you order any of the variants of the Codex you get Genestealer art cards!