Robin Hard's version of "The Library of Greek Mythology" is one of several modern English translations of an ancient (date disputed) compilation (*bibliotheke* - hence "library) of summaries of stories of the gods and heroes of Greece (but not Rome). It seems to be based, wherever it can be checked, on excellent sources; or, possibly, on earlier compilations which had excellent sources. It was not intended for pleasure reading, but for use as a reference manual, although we have evidence that in Byzantine times some readers used it as a short "history" of mythological times.
If the name of the author is correct, he cannot be the "Apollodorus the Grammarian" to whom the work used to be attributed. Unfortunately, this is the only name we have for it. Given the lack of internal fraudulent claims, however the bare name seems to me better than "Pseudo-Apollodorus," as it is sometimes given, since "pseudo-" is likely to be taken as a reflection on the author, instead of early scholars.
Considering the huge amount of ancient Greek literature that has been lost, and the primary sources to which this compiler (whoever and whenever he was), seems to have had access it is even more regrettable that a portion of "The Library" survives only in an abridged form. (Fortunately, part of the re-summarized material is Homeric; unfortunately, some of it is not.)
Hard's translation is a clear presentation of the material, with an excellent introduction and helpful notes, as one would expect from the Oxford World's Classics series in recent years. It can be read alone, consulted, or, I think, used as a class text (not in my personal experience, however.) It is not the only translation available.
The "classic" translation (which stood alone for half a century) is that by Sir James Frazer (of "The Golden Bough") in 1921, in two volumes of the Loeb Classical Library (and so facing a Greek text). His commentary to "The Library" is, as one might expect, packed with information from other ancient sources and later parallels. Unfortunately, Frazer's commentary is not very well organized. His translation - to my taste - adds a certain Victorian ponderousness to the spare, and sometimes awkward original. (The use of Latin names for the deities and heroes may puzzle the novice, and annoy those of us who grew up on Greek names for Greeks.) This version is still in print, and is available online at the Perseus site (for classical literature, etc.), and PDFs of the two volumes can be found at the Library of Congress site (archive.org).
1975 and 1976 saw the appearance of two new translations, by Keith Aldrich and Michael Simpson, respectively. The Aldrich translation, as "The Library of Greek Mythology," is out of print; Amazon seems to offer current printings, but these turn out on inspection to be the later translation by Robin Hard.
Simpson's "Gods and Heroes of the Greeks: The Library of Apollodorus," is still in print. It is a richly annotated on ancient and modern literary versions of the story. Simpson has been criticized for unspecified inaccuracies in his treatment of the Greek. The most recent translaters, Smith and Trzaskoma (see below) prefer Hard's translation. However, Simpson's translation is clear, and his annotations, on the whole, well organized, if sometimes losing track of Apollodorus' text. Some readers seem to have found the language too American for their taste. It should be remembered that the author, whoever he was, used a kind of "international literary Greek," which probably seemed fairly up-to-date (if not very elegant) to his well-educated readers. Whether academic American English is a good substitute is certainly arguable.
Simpson's commentary appears as end-notes to sections of the main text, which makes for frequent interruptions, and the index is a bit sketchy, although usually helpful. I have used this edition for a quarter century with considerable enjoyment, and frequent enlightenment about other ancient works, and modern ones.
Aldrich's translation does not discuss other ancient versions in any detail, or refer to modern literary versions. I found it quite readable, but as of a decade ago I much preferred Simpson's version -- possibly a consequence of owning a paperback copy, instead of consulting it in a library. (Both Aldrich's and Simpson's versions are also illustrated.)
The more recent (1997) translation by Robin Hard, in the Oxford World's Classics series, as "The Library of Greek Mythology," has textual notes and critical apparatus, aimed at fellow classicists, but comforting to some of the rest of us. Hard's introduction and commentary offer clearer exposition of the structure of the "The Library" (stories arranged regionally, and genealogically in each section -- the latter device going back to the Hesiodic "Catalogue" poems, centuries earlier). It also has a superb index (several, in fact), and is fairly good on ancient variants, but avoids treatment of modern versions of the old stories, which is Simpson's strength. (Hard is one who does not approve of Simpson's translation.)
This translation is, like Simpson's, in print, and it also is now available in Kindle. I found the digital edition to be well-designed and well-executed, when I read it this spring on a smartphone screen, which I consider the ultimate test. (Toggling back and forth between text and notes took some time to get used to, but that was my problem!)
A more recent translation, aimed largely at students, is "Apollodorus' 'Library' and Hyginus' 'Fabulae'" translated, with Introductions, by R. Scott Smith and Stephen M. Trzaskoma (Hackett 2007), also available in both paperback and Kindle formats. It contains complete, and substantially revised, versions of material which had appeared in excerpts in the same publisher's 2004 "Anthology of Classical Myth."