We got maybe one bib/hat combo for the table (which my younger daughter snagged). No song books, no live music/dancing. We got to the Bolingbrook location around 6, and there was already a massive line. For what it's worth, many of the Asians in line seemed to be part of a few large groups, to the extent we wondered if there had been a hired bus; lots of mingling, place holding, cutting in queue en mass. The kitchen didn't seem to be lacking food, even though we did indeed see people greedily piling multiple plates full of crayfish at a time. A few times the line seemed to stall (after we were sitting) while they waited for more crayfish to come up, but never for long.
There was a lot of pushiness at this location, too. But the staff (per IKEA standard) was surprisingly affable and helpful, and, most importantly, organized.
Personally, I thought the crayfish were inedible, both literally and figuratively. Minus any sort of cracker, I just couldn't get into the shell without risking slicing open a finger. But since they tasted like dill brine and little else, we didn't feel like we missed out, and in fact were happy sticking with the salmon. I'm not sure I saw anything served that you can't simply pick up in the cafeteria most days or frozen in the market by the check-out, possibly including the crayfish but definitely the shrimp and salmon. My daughter was mostly disappointed at the lack of Swedish fish on the menu.
Basically, we're happy to have done this weird thing once, but are happier to never do it again. It was like Disney World with worse food and no rides.