Not so much a sudden wrap as leaving-off-with-a-future.
Many, *many* first-authors suffer from "Happily Ever After" syndrome, in which all the significant threads are wrapped up on a paragraph-by-paragraph basis. Each one plotting out a lifetime. As you can guess, it's kind of disappointing to read. Almost as bad as "and they went" narrative.
I disagree, most heartily, with the presumption that having a non-tragic ending is in any way amateurish, or that it is in any way the sign of a 'first-author' to have a happy ending. If you want a nihilistic ending, go read our other book, the dark, pitch black comedy 'Urban Gorillas', here: http://jenniverse.com/urbanmain.htm
We could not sell that book because, although several publishers were interested, it was rejected for being 'too dark'.
There is nothing wrong, whatsoever, with an ending where the protagonist triumphs. Indeed, outside of Greek tragedy, it is the only satisfying ending - only the most Emo would wish for endless stories of losers and how they failed. Life is full enough of that, dispensed to all of us, throughout our sad lifespans. The point of heroes is that they succeed, the point of a story that is not a tragedy is that it shows us that, occasionally, things can go right. At least for someone
I am sorry you are disappointed. But I am disappointed in your outlook, the superior sounding dismissal of a successful ending for a protagonist as an amateurish thing. What the hell crap have you been told that you would think that a happy ending is anything other than appropriate?
As for the protagonist, Tala, yes, she has a city now, and she owns it. For now. But a sequel, if one were ever to be written (not likely now, because, let's face it, what the hell would be the point?) could easily explore just how hard it is to hold on to what one has, and how very fleeting success actually can be. A thousand and one things could go terribly wrong. Isn't this how 'great' works, like the original Star Wars, and Back To The Future, and many more operate? First movie is an apparent 'happily ever after', and if there is a sequel, everything goes horribly wrong, only to be corrected to a final, truly happy ending in the third installment? And what of countless individual novels that end on success, from the works of Asimov to Heinlein? Oh, yeah. That stuff. The entire history of modern literature and film.
I don't expect rave reviews, but I do expect cogent complaints, and complaining that a positive outcome is amateurish is just plain silly.
What a world, where it is expected that the 'professional-level' writer is defined by books that inevitably end in a way that makes the reader feel brought down, where the protagonist is seen to be a failure, ultimately, and everything turns to shit in the end. Yeah, that's some fine readin' there boy. Sweet. Or the notion of endless, joy-leaching chapters that follow up minor crap piddling off beyond the proper, triumphant ending.
If that is 'professional-level', then I am going to stick to the 'first-time' amateurs, like Clarke, and Heinlein, and Pohl, and Sheckley, and Asimov and Leiber and Norton, with all of those silly happy endings where the hero triumphs in the end, and minor secondary matters, relatively unimportant to the main plot, are wrapped up succinctly -so as not to leach energy from the triumph of the protagonist.