Slaanesh is the smallest mono-chaos God book, that's for sure. The mortals not being there feel like a missed opportunity, but this release does tie you over for a couple of years I suppose.
I was a bit let down that the FEC only got a single hero, spells and terrain. but then I remembered how much work I still have with all my nighthaunt, Legions of Nagash and shadespite... And warcry is going to be added to the mix. So, my initial sadness of "not that many releases" oddly made way for being happy that the FEC feel quite "complete" for a change. After a bit of that sinking in, I was actually quite pleased.
I'm just not sure how well the hedonite rules will interact with slaves to darkness (who will surely be getting an update soon). Jess (on Stormcast) essentially said the focus would shift back a bit to chaos after all this death stuff.