I see that this thread is a bit old, but I'd like to voice my opinion since I've been blessed by the writings of Watchman Nee.
"The Normal Christian Life" is his most famous book, and it's also the one that I'd recommend if someone were to read only one of his books. It's a brilliant and immensely deep book that has been a great help to me personally. It's one of the few modern Christian books that can be called a “classic”.
Another book of his that perhaps is a bit underrated, is “The God of Abraham, Isaac and Jacob”. It's an original and fresh take on the story of the patriarchs. Highly recommended!
I agree with what paul1149 wrote earlier in this thread; the only book that I probably would steer away from is “Spiritual Authority” and he definitively goes too far in that book! However, I think the accusations of “cultism” are very unfair! As has been mentioned before in this thread, Watchman Nee was a Chinese believer born back in 1903, so it's no big surprise that traditional Asian ideals coloured some of his views on authority. My feelings is that this is first and foremost a cultural issue, and to accuse him of cultism is to demonstrate a complete lack of understanding about how Christianity manifests itself across different cultures. Even today you'll find that believers in Asia often have very different views on authority than we do here in the west. It's probably true that some people have used this book to justify a Church order that is overly authoritative, but that's no valid reason to dismiss him as a thinker. An example: We're all indebted to Martin Luther, but do we necessarily agree with every single line Luther put on paper?
Watchman Nee was persecuted and languished for a long time in prison, and it's even possible that he became a martyr in a literal way. When he died his body was cremated before his family could see him, and in his departing note he wrote that he died because of his faith in Jesus...