Usually a prequel no matter how good can never be standalone because it relies too much on people understanding the original work to help it make sense or at the very least streamline details.
I love Star Wars: Rogue One a lot, but if you had never seen A New Hope or any other Star Wars work there would be a lot of moments that would give you pause or make no sense if you never seen the following films. (Also don’t say the Star Wars prequels because while they’re fairly stand alone, they’re also not good)
Godfather 2 would fit the bill for me, EXCEPT it’s only half the movie and the other half is the direct sequel to Godfather 1 so you would have to watch Godfather 1 for it to make any sense.
So are there any good prequel works that are completely independent of the original?
The poncho? I think Leone just dropped that in at the end of the film so fans would have something to argue about on the Internet fifty years in the future. A very prescient man, Sergio.
Small Gods, the 13th Discworld novel, takes place a couple hundred years before most of the preceding books, and is one of the best in the series.
Steven Brust’s Taltos Cycle books weren’t written in chronological order, with each book jumping backward and forward in the life of the titular assassin.
The Virginians by William Makepeace Thackeray is a quasi-prequel to Pendennis (as well as a sequel to Henry Esmond); it’s about Arthur Pendennis’s friend’s grandfather and other extended family. It basically stands alone, although there’s one or two bits that might be slightly confusing if you haven’t read Henry Esmond.
That’s kind of a special case, since the source material was written and published first.
Even so, there were some things that Peter Jackson stuck in that, it seems to me, viewers who hadn’t already seen LotR wouldn’t fully appreciate (like the framing opening with cameos by Ian Holm and Elijah Wood). I do wonder whether which trilogy a newcomer should, ideally, watch first, if they’re going to watch both.
Prey counts I think. As well being a really good movie it stands alone and you definitely don’t need to have seen the original Predator for it to make sense. There are a few allusions to the original you’ll miss but it won’t effect your enjoyment of the movie.
Yeah, in the later Guards books, there a character in the watch, Visit-the-Infidel-with-Explanatory-Pamphlets, who worships the reformed Omnian religion, after Brutha did away with all the thumbscrews and hot pokers. It’s possible that Brutha’s reformation spread all the way to Ankh-Morpork in just a couple years, but the ending of Small Gods where Brutha dies of old age implies that he spent most of his life reforming the church, so that book probably took place much earlier than Guards! Guards!, which was the eighth book published.
Oedipus Rex, a prequel to Antigone which was written first.
A Stainless Steel Rat Is Born. Harry Harrison began his series with Jim as an adult criminal with years of experience. Born is a later prequel, telling how young Jim began his career. It’s the first of the series that I read, it did not require any knowledge of later events, and IMHO the best book of the series.