My players enjoyed this; but it was tough to run.
1) Very strong suggestion: remove/avoid asking the adventurers to figure-out how the substance is being smuggled into the city. There's no plot to follow here even though the module text suggests this as part of what the quest-giver asks to party to do.
2) Be aware that a moderately crafty party can shut down the chase scene very quickly (less than three turns)--so be prepared with some other outcome or pay-off for the set-up of the theft.
3) If you know your players like scheming and plans and a good infiltration game, have some notion of what the final village looks like. Let them sneak in, avoid guards, and get some advantage for the final fight rather than just dumping the party in the middle of the evil ritual scene.
I think final battle is fun. My group liked the "reveal" of how the grungs were involved and the monsters are fun to run. Review the tactics available to the tribal warriors; it makes them much more fun to run!
[3 of 5 Stars!]