This is brilliant. The whole thing is brimming with fresh ideas, and best of all, shows a real understanding of the product. So many elements dovetail back into and enhance the lore. McGovern knows our book back-to-front, and having read through his supplement, I'm 100% sure I'll be using it in my next campaign playthrough.
1) A complete 30 day schedule of jungle events for travel that really enhances the story. Learn to form your own battle stack (!), endure a literal rain of zombies, explore a temple of Ubtao, avoid zombie swarms, and learn to fear the Sewn Sisters - the deadly penultimate-nemeses of Tomb of Annihilation. Overall, it's perhaps a little lacking in combat challenges, but more than makes up for it in thematic colour and roleplaying opportunities.
2) A list of additional Omu locations that build on the lore of the city.
3) Magical enhancements for each of the legendary treasures listed in the Tomb of the Nine Gods.
Yes, there are some typos and odd turns of phrase, but the breadth of content here easily outweighs those minor issues. Highly recommended.