I really liked the overall design choices, I think starting with the hermit who leads them through the ruins up to The Voice is the right choice and sets the mood well. I didn't love the motivation, though. I thought that transforming into yuan-ti wasn't strong enough of a motivation to "solve" the problem. I love the adventure within the overall setting of ToA. I run the campaign, and I've added a lot of additional AL content, and a lot of it has to do with different yuan-ti plots. The fact the yuan-ti left Hisari and found refuge in Omu is crucial to the plot of ToA. If it weren't for that, they wouldn't have met Ras-Nsi. Also, because it happened 50 years ago, yuan-ti captives could actually give information about that, and so the PCs heard about Hisari, and it was one of the "mysteries" of the campaign. They really wanted to get there and find out what happened. I liked the back story. The hubris of the priests trying to summon a version of their god. How the yuan-ti, once proud to be selected by their gods, were actually abandoned by them. How of their plots are moved by this despair. Eventually, though, the PCs aren't doing much more than killing a monster. It's a very entertaining monster set in a suitable dungeon, but that's it. You would note I'm ignoring the whole "yuan-ti can't feel" sidequest since I didn't incorporate it in my game.
[4 of 5 Stars!]