Unwind "Dystology": Standalone Novels vs Series

Quite a few years ago, I picked up a YA novel called Unwind, written by Neal Shusterman.  It's one of the most compelling YA novels I have ever read.  In many ways, it reads like scenes of a movie -- present tense, action-packed, and showing different points of view even from minor characters.  This all culminates into effective world-building and one thrilling story that kept me engaged the whole way through. 

The story takes place in a futuristic (but still very recognizable as our own) society in which medicine and science have progressed to the point of making all body parts viable for human transplant.  Arms, legs, eyes, brain and other internal organs -- all of it can now be removed from donors, stored, and surgically grafted onto needy recipients.  This medical advancement and the Second Civil War (a war between Pro-Life and Pro-Choice citizens) have resulted in a compromise of sorts in society.  Abortion is now illegal, but parents or guardians may now legally elect to have their 13-18 year olds "unwound" -- a process in which they are surgically dismembered but in which all their body parts will "live on" in transplant recipients.  The story centers on Connor, Risa, and Lev -- Unwind teens trying to escape that fate and survive until 18.  

The novel touches on many social issues, like how social conflicts of the present can affect future generations, ethics of law, right to life, abortion, and even theology such as the concept of the soul.  Even though it discusses these heavy issues, it never attempts to sway.  This is the story of the characters, dealing with the world and the law as they affect their own lives and destiny.  Every chapter moves the story forward, giving no time to linger and very little breathing room.

By the end of the novel, I was satisfied.  It was compelling and refreshing to see a standalone novel fulfill me so much.  These days, it seems like true standalone YA novels don't actually exist.  Nearly everything, and certainly everything popular, is part of a series.  I championed the book not only for its amazing storytelling but for that reason as well. 

And then, years later, it was announced that it would be a trilogy, which later turned into a series of four (not including a short novella e-book) when the third book ran over 600 pages long.  The mixed feelings I had about this were understandably intense.  I wanted more of that world, more of those characters, just more in general.  But Unwind had felt so complete and I just wanted to believe that amazing standalones could exist in the world.  And then Unwholly was released and I fell right back into it; the same quality of writing, but with old and new characters, and old triumphs heralding new problems and -- it was amazing, once again. Even if some elements of the world-building did feel a tiny bit tacked on.

Overall, it was great storytelling and I cannot wait for the next book to come out in just a couple short weeks.

But I do still wonder if standalones can ever hold the same kind of appeal and popularity of a series, and whether this is good, bad, or just the way it is.  Are there any series you believe could and should have been standalones, or visa versa?  Do series become more loved simply because readers get to spend more time with the characters?  If you find out a book is part of a series, does that make you more or less likely to check it out?

Feel free to sound off with a comment and check out the Unwind series while you're at it.