Stick with Lonely Planet
I bought both Lonely Planet and Moon to be able to get a nice perspective on my trip to Costa Rica. Unfortunately the Moon handbook was not as useful as Lonely Planet. In fact, by the middle of the trip I buried this book at the bottom of my backpack. The only thing I found useful in Moon's guide was its maps. Other than that, I would stick with purchasing Lonely Planet.

Most informative
We have three current travel books on Costa Rica - this one is by far the best. It provides a full range of options from budget to luxury. He gives detailed reccomendations,insights, and cultural background. And it just seems to provide more complete coverage than the other books.

A weak alternative to LP
I just returned (7/08) from a trip to Costa Rica. My sister and I had the Moon guide as well as the LP. Although LP's guide bears an older copyright date, it was the Moon guide that seemed out of date, and it contained many errors, ranging from incorrect phone numbers, to badly out of date prices, to outdated hotel descriptions, to listing no-longer-existent tour and transfer companies. It basically became dead weight in the baggage.

An example: the Moon Guide discourages individuals from visiting the Aviarios del Caribe sloth rescue center, near Cahuita, alleging that it now only welcomes cruise ship groups. In actuality, my sister and I were warmly welcomed and given a wonderful tour -- a highlight of the trip. (And: the admission fee was much lower than what Moon listed.) Travelers following the Moon guide advice would miss out on a wonderful experience.

I don't know the author's actual research methods, but I sometimes had trouble believing he had personally visited many of the hotels and restaurances he describes; I suspect heavy reliance on user feedback.

Costa Rica is certainly changing fast -- in general, prices were significantly higher than either Moon or LP listed, and hotels tended to have been upgraded. Towns listed as not having banks, in fact do. I can't believe, though, that all the changes we saw had happened just in the year or two since the Moon guide was supposedly updated.

Not for LP loyalists or budget travelers
As a loyal Lonely Planet reader, I thought Moon would be as good or better, considering the reviews for the two. This book is written for the author's ideals only - anyone who is really into sportfishing and seeing exclusively expats while traveling. It does a poor job of listing the more budget-minded lodging and restaurants, and has little to no mention of info that would suit someone with cultural interest. All restaurants and lodging are "to avoid the Ticos, book here" or "try expat Chuck and Susan's pace, here". It would help someone book an entire trip to see other travelers traveling, and to go fishing. Disappointed, I went to the bookstore and paged through LP's older, more concise guide book, and was thrilled to see better descriptions, more color pictures, and more cultural insight. Moon's book also packs an extra 100 pages of Costa Rican history - something that is nice, but not necessary to take with me in a backpack trekking around the country.
Lastly, the author has an absurd overuse with superlatives! "This beach is the best in the country" and "the wildlife in this park is unmatched" - these are good descriptions, but when applied to every park and every beach, given that there are dozens, it makes it difficult for the traveler to make an informed decision to organize their best trip to Costa Rica.
Overall I was disappointed and will be buying a different guide book to take with me.

Thumbs Up for Moon Guidebook
Extremely happy with this guide book. It is very well organized and seems complete. The authors will tell you their favorite places as well as ones to avoid. Has phone numbers and websites (if available) for most of the hotels. Quite a few pictures included. Totally worth the money.