The best Hack supplement I have read. Excellent introduction to the classic Empire of the Petal Throne setting. The classes, magic system and other rules are elegant and clearly laid out. Highly recommended.
The Hack system is generally good, especially for those who lack the time for a fully involved RPG campaign. I was pleased to see "Petal Hack", as "Empire of the Petal Throne" is a sentimental favorite for those who remember gaming in the 70's.
This may be the clearest introduction to the world of Tekumel Ever. There is certainly more you can know, but this will give you a good start and the Black Hack system is filled with Old School goodness.