What is Reddit's opinion of The Haiku Handbook#25th Anniversary Edition: How to Write, Teach, and Appreciate Haiku?

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Sort of. The rules for English haiku are slightly complicated because it's fundamentally a Japanese poetic form that we picked up and started using for some reason. As a very brief overview, in English, the following criteria generally apply:

• It should be three lines, with the general guideline of short-long-short. (There are other words for poems with the same semantic elements but different structure.)
• There should be a juxtaposition in tone or theme between the first two lines and the last one. This is the concept of kiru from Japanese haiku. In Japanese, there are lists of words to be pulled from to denote this, but listing words in English is a fool's errand, so we just get wishy-washy conceptual guidelines. =)
• In Japanese, there are lists of seasonal words you're supposed to draw from, but again, English is not a good language to list words in. English-language haiku often use season as a thematic element, but it's not strictly necessary.
• As a final super-abstract point, a haiku should create a sense of presence in the reader. It's supposed to be describing a place and time so you can feel yourself there, rather than e.g. chronicling an event.

There are very good books about English-language haiku if you're interested in learning more. I'll recommend The Haiku Handbook as quality and comprehensive.

For anyone interested in haiku, I highly recommend Higginson's Haiku Handbook