First, the two seasons were really dark (not that I am complaining). The third and final season was really boring. All the hide and seek, catching, and releasing really bore me up. Also, I expected a clean and proper ending. I hated how Will's character developed to be and also it bothers me that he calls Hannibal his friend. Alana Bloom, I hated her in season 2 for being such a blind moron but in season 3 she was a badass.
Also, the series is not having any spin-off, then what's the point of a cliffhanger?