I've got it. Only played the levels that were in the beta so far. With 3p local co-op, the game is a blast. Now, the thing is, we spent most of the time slapping each other (off ledges) and painting each others' faces with stickers, but just running around grabbing at everything, and racing to collect the little orbs was all good platforming fun. I still find the controls a bit floaty, but you get used to it.
Yeah, 'casual' appeal, but for the level-builder, the toolset is very powerful, while still remaining fairly easy to use (though if you want to make some complicated/detailed, it can be pretty time-consuming). This is one aspect of the game that the casual community won't touch much on, but that's the beauty of the game. Accessible to people who want to build complex levels, and accessible to people who just want to jump in and play. Community levels are apparently fairly easy to find. Co-op toolset is an awesome feature, and Nick and me will be brainstorming there.