As has been stated by most readers who have commented here, the end was a shock.  I have read similar reviews everywhere.  I have only read two books by Sylvia Day .that were not part of the Crossfire series so I do not know her style.  That being said, I have read hundreds of romance/erotic romance/erotic novels during the past few years.  For me, One With You reads like an edgy Nora Roberts.  If I had been reading one of Nora's books what happened to Monica would not have been as much of a surprise.
Normally I would have expected the lives of all the characters to be tied up with neat ribbons but I think Sylvia said in an interview about this book that might not happen.  I, therefore, was not surprised to find so many characters unfinished....too many for my early expectations of the series.
A sixth book that provides a traditional/typical ending would take away from what I consider a unique ending to the Eva/Gideon story. Â We are left to fill in the future for ourselves.
My comments should not be construed to imply I am happy.  I wanted a warm, fuzzy HEA.  I do thank Sylvia for a special reading experience that makes Crossfire a standout among the books I have read.Â