Reviewed in the United States on August 5, 2014
There were fewer than 84000 words of length 2 through 8 in the previous edition, and this one claims 5000 such words have been added. So the claim that there are over 100000 such words in this new edition is false.
Of course, what is urgently needed is a book that claims 75000 (or whatever the number turns out to be) REAL Scrabble words, in accordance with the pre-1976 rules that made the game wildly popular; in accordance with those rules, such a book would be based entirely on 21st-century dictionaries. It's overwhelmingly likely that you do in fact play with the classic rules. The 1976 changes were implemented by a group of New York City "experts", predecessors of today's North American Scrabble Players Association (NASPA), who invented a game unpopular even with New Yorkers (the second-largest bridge club on Manhattan has more members than NASPA does throughout the continent, even though all polls show Scrabble to be slightly more popular than bridge!).
According to the classic rules that made the game popular: "Any words found in a standard dictionary are permitted except those capitalized, those designated as foreign words, abbreviations, and words requiring apostrophes or hyphens. Consult a dictionary only to check spelling or usage." Consider whether OSPD5 measures up.
"Foreign words" -- there are about six dozen OSPD entries marked foreign in the only dictionaries that listed them. Some are immediately recognizable as foreign: YOM JEU URSA PADRI ESPANOL etc. Believe it or not, DE is listed as a preposition found in foreign surnames meaning "of; from"; there used to be more. Up-to-date English dictionaries now exclude words requiring the label foreign. OSPD provides no warnings, so you'll be hard-pressed to follow the classic rules with OSPD.
Actually there are more than a thousand foreign entries in OSPD if you include Scottish words. In 1953 co-inventor and popularizer of the game James Brunot authorized "The Scrabble Word Guide" based on a dictionary with lots of Scottish words; none were allowed. Indeed the majority of OSPD Scotticisms arise from the 1973 printing of the 1962 edition of that dictionary, which went out of print a third of a century ago. Some are instantly recognizable as Scottish: AE JO GAE GIE etc. Others might not be: VOE GED etc. OSPD provides no warning. Do you enjoy Burns's poetry? OSPD lists only about half the Scottish words found in the glossary of a recent edition of his poems. Scottish spelling has undergone changes in recent years. Virtually all your opponents will regard Scottish as foreign.
The rules certainly imply "standard ... spelling" and "usage". There are many dialectal words in OSPD, some recognizable, like UN (one) or CHIMLA; others not, like MIB or MUN. Many new entries are used only in remote parts of Canada, similar to many holdovers used only in isolated parts of the U.S. or U.K (e.g., VUM, from New England; I'm from there and have met it only in novels older than Scrabble). Such words were not a part of the authorized 1953 list. Obsolete words were likewise excluded, as well as the few offensive words found in the 1953 dictionary: such items are not standard usage and are not permitted by the classic rules.
KNESSET is a capitalized word which was left uncapitalized in the first printing of an old edition of one dictionary. Needless to say, a year or two later the second printing made the correction. OSPD perpetuates the typo anyway. (UMBELULE made the previous edition of OSPD due to faulty input from NASPA -- it remains in OSPD even in this new edition. Merriam appears to treat this opuscule with contempt.) PRIE-DIEU is a hyphenated word so spelled in all but a long superseded edition of one dictionary. Likewise for at least a hundred OSPD entries.
Possibly the worst problem with OSPD is that you cannot find many entries in a standard dictionary any more. Aside from a few typos, entries could be found in at least one dictionary (often only one, contrary to what you may read elsewhere). But language changes; lexicography improves. Many spellings obsolescent a half century ago have disappeared from all current college dictionaries, but are retained by OSPD: PUR, JIN, OXID are three among hundreds. The 1969 first edition of one dictionary showed ES as an also-ran variant of ESS (but not at its own alphabetical place), but later editions excluded it. AL appeared in one dictionary in print for the first OSPD, but was overlooked (and missed by no one); it was noticed in time for the second OSPD, printed just months before AL was excluded in the new revision of the standard dictionary. Lexicography has made much progress, especially with the aid of computers, since the first edition of OSPD, but NASPA refuses to take advantage or to acknowledge that the English language, like all languages, discards old words while adopting new.
Suppose, like 99% of Scrabble players, you play the game in harmony with the classic rules and wish to continue doing so; in other words, you enjoy REAL Scrabble with REAL English words. OSPD could never be your only resource, since words longer than eight letters are to be looked up in a standard dictionary. As shown above, OSPD doesn't honor the classic rules or current standards of English anyway. Your best choice would be the 5th edition of the American Heritage Dictionary. All forms of most verbs are shown explicitly, and a sensible selection of adjectives are shown with the -ER and -EST endings, so that you can accept VAINEST or PLAINER while rejecting MAINEST. This dictionary excels in numerous other respects, some with direct relevance to Scrabble such as inclusion of words omitted by OSPD. (A few examples of words that have come up in my everyday life and in Heritage but not OSPD: GICLEE HAMERKOP INNIE OUTIE VUVUZELA.... Your own examples will differ, but you can find them.) American Heritage exemplifies current standards of spelling, hyphenation, and capitalization well. The only other dictionary edited in North America that can be suggested for Scrabble is the Merriam-Webster Collegiate, and its only advantages are price and hyphens that are better than flyspecks. It has been in its 11th edition for a decade or so, with some annual updating, and for the most part you are on your own for inflections. Rest assured that any typos discovered in the first printing have long since been corrected.
I think this fairly describes OSPD so that you can decide whether you want to buy it. If the above seems much ado about nothing to you, then please investigate NASPA. They need you. The American Cribbage Congress has more members on its website than NASPA has ever had paying dues at any one time; the American Contract Bridge League is a hundred times more successful in attracting bridge enthusiasts to its activities than NASPA in attracting Scrabble players. OSPD is a large part of the problem.