Review edited on 4/11/18 to give a bit more info:
First of all, I love the story and the setup of this adventure. The writing is solid and the descriptions of the world and characters are very strong. The adventure is laid out fantastically and was very easy to follow and prep. Well done!
I ran this for my group of 5 level-4 PCs this weekend, and we did have fun. We also identified some issues that could be addressed. One of their biggest criticisms was that the introduction of the first NPC (Kara) set them on edge and prevented them from just enjoying the lavish party. From the beginning, they were looking for trouble and this prevented them from really "playing." Also, because they had been warned that something was afoul, only two of them put on their magical masks. They cast "detect magic" on the masks right away, giving the game away. Later, the PCs who hadn't put on the masks felt left out because they didn't get cool abilities. I think the players questioned why other guests turned into hybrids but the effects of the PCs' masks were slower; I'm not sure how to address that, but it did seem like a lack of consequences for choices.
There were some moments in which the NPC setup was a bit complicated - the drinking game portion has a handful of NPCs with secrets, some drunk, some not - and for me, it was a lot of motivations and personalities to juggle at once, while also engaging in a fake drinking game with the PCs. My group is usually very silly, but they just didn't get into this, I think because I wasn't sure how to properly run it.
The Big Bad is very fun. I modified him a little to be more challenging for my group, but the players seemed to really enjoy him and his story - and the reveal at the end from Kara. Overall, it's a great story and worth purchasing even if you end up modifying it a bit. Most importantly, I recommend that the reveal about the bird man's death come during the party - not before - so that the PCs can enjoy the festivities without suspicion.