Hell yes it's worth it. Nice, concise, compact book (it's not really all that "big") with great photos. I have a Zinn book too, which I also like. The Zinn book has illustrations which I don't like as much as the Park book's photos, but it is generally more in-depth. I'm referring to Zinn & the Art on Mountain Bike Maintenance.

Make sure to get the 2nd edition of the Park book.