I thought the ending was incredibly sad and fairly justified.
Anyone notice the contrast in setting between Dexter and Hannah+Harrison during their last phone call?
In Dexter's world, he was in a deep dark storm, surrounded by an army of thunderous clouds and lots of pain.
In Hannah+Harrison's world, they were in a heavenly paradise, with the sun shining and the bird's chirping.
I didn't think it was the worst finale. They killed off Deb after the doctor was optimistic, and Dexter pretty much lost everything. While it could have probably left me more satisfied, I think the series in its entirety was fantastic.