Lonely Planet (LP) has introduced a new line of guidebooks, the Discover series, including this one. To me they seem similar to the DK series - lots of color photographs, less text, attractively designed, glossy paper, usually one topic per open pair of pages, but that one topic is covered quite well. Color is used for the edges of pages, to make it easy to find a section for the part of the country you are visiting. Overall the graphic design and use of color of whitespace lends both excitement and useability to the guide.
Unfortunately, there appears to be confusion about this new LP series. Although each LP Discover so far covers one country, it does NOT replace LP Country Guides. Some people have bought it thinking it is a new look for an updated country guide and are not happy with it - "This is horrible, this is like a travel advertisement, I'll never buy another LP again, etc.". Needless to say, it is not for everyone. Fortunately, you have a lot of choices in the best guide for YOU, so...
There are many to choose from for your trip to Thailand. There are several from Lonely Planet (LP), plus there is the Rough Guide, DK, Frommers, "Travelers Tales" and "Culture Shock". Start at the library or a big bookstore and look them over briefly.
I usually prefer LP, not because it is better than Rough Guide (for some places, Rough is much better), but because LP is available for more countries. Because the style is consistent, I can quickly find what I need.
Now LP has TWO country guides for Thailand: LP Thailand (LPT) with 820 pages, and the new "LP discover Thailand" (LPDT), a.k.a. Full Color Country Guide, at 408 pages; LPT is larger but they weigh approximately the same. LPDT is comparable to DK: lots of color pictures, beautifully organized, larger type, nicer layout, heavier paper. Like DK, I think it is best for reading before you go, even before you decide WHERE to go. If your library has LPDT or DK, you might start with them, and then buy the LPT to bring with you. If you are only going to Bangkok, or the beaches and islands, LP has guides for these destinations that have even more info than LPT.
LP DISCOVER THAILAND (LPDT) vs. LONELY PLANET THAILAND (LPT)
This section is about comparing the two books without value judgements. I am not saying one is better than the other here, rather that one book may be better for you than the other. In particular, more is not always better. For example, if you have time to see only one site, and not a lot of time to read/research, it is useful to have the book present the most popular highlight. Other people want to see more choices and make up their own minds. Both styles are useful.
Since LPDT has half as many pages as the standard guide, has larger type, more pictures, more white space, you would guess correctly that it does not have as much information as LPT. Mostly, it has the same KIND of information as LPT - where to go, how to get there, how to get around, where to stay, what to do, entertainment, food info, dangers, annoyances, health risks, etc - most of the basic info you need to get around. But LPDT has much less info than LPT, and it lists fewer actual locations.
I'll use Phitsanulok for comparison. It is not a primary place to visit, but I enjoyed visiting there; it is covered in both guides. LPDT has fewer than 4 pages, part of which are used for pictures; it has 1 paragraph for 1 temple and a brief mention of a few other sights, lists 5 hotels and 6 places to eat, discusses only the city, and has no city map. LPT has almost 9 pages, describes 2 wats in about one page of text, covers the city plus nearby areas in the province, includes a detailed city map, no photos, and lists 17 hotels and 11 eating options. If you had a day in Phitsanulouk, LPDT is fine. Others would prefer the additional information in LPT, to see more or have more choices. [Note: I used LPT 11ed 2005 for this comparison.]
LPDT has 46 pages for Bangkok; LPT has almost 100 (including daytrips around Bangkok). LP Bangkok has 296 pages.
LPT describes many more locations in Thailand than LPDT. LPT has 83 pages on Northeastern Thailand (Isaan); LPDT has 26. LPDT excludes Udon Thani, a mid-sized city to the north popular with ex-pats. This does not make LPDT worse, because the places that have been excluded are not primary places to visit. While choices for cutting were probably difficult, I think they chose reasonably well.
LPT has 12 pages on the history of Thailand, sections on food, and some but not many color pictures. LPDT and LPT weigh approximagely the same, but I estimate that LPT has 3-4 times as much information but far fewer pictures. LPT makes compromises on the paper, pictures, type size, layout, white space, etc in order maximize the amount of useful information needed during a trip. LPDT is more glossy (one reason it weighs more).
WHEN IS LPDT USEFUL?
For a first time traveler, especially if you have limited time or prefer fixed itineraries, LPDT (or DK) might be all you need for your trip. LPDT and DK are great for a traveler who is unfamiliar with a country; they give you a good idea of what you will see, which helps you decide where to go and learn a lot quickly.
I have been to Thailand several times, but I still find LPDT useful to find parts of Thailand I have not yet visited, with pictures to help me plan which ones to visit. But I will use it at home, and bring LPT with me.
For people with middle-aged eyes, LPDT is easier to read with its larger type, whiter paper for more contrast, more white space, and color coding to navigate more quickly, though LPT isn't that bad.
For me, both the LPDT and DK guides help me decide where I want to go more quickly with pictures and easier organization, but I bring LPT with me instead because it has a far more information. I prefer to travel with only a rough plan and make it up as I go, so having LPT with me is essential. It also helps when problems come up - something is closed, there is bad weather or trouble, etc.
All of the books I discussed are good, but their purposes and depth of information vary considerably. Buying the right one for YOUR needs is worth a bit of research.
NOTE: I am an Amazon Vine reviewer. This book was provided to me free for my review, but I am not paid. My opinions are not influenced by getting a free book, nor am I asked to write positive reviews: I call them like I see them. I have been to Thailand more than a dozen times and have spent a lot of time in many places. I know the country reasonably well, speak some Thai, and I have read most travel books about this country.