User blog comment:Maimer1882/Cliffhanger/@comment-4818381-20120218201328/@comment-3146930-20120219001847

What I mean is that at the end, Percy and Annabeth were together and the big bad was defeated with no hint of a new bad guy (unless you count the new great prophecy). However, in the book they say it may not happen in their life time and there was no hint of a sequel so it wasnt really a cliff hanger.