Maintaining silence on the last episode.
Immortality has been around a long time in fiction, especially SF, but they've really thought it through, what it would truly be like if no one ever died. What I miss in the series is the bizarre, the mystery, the weirdness. Given the one basic "What if...," the rest of the show is mostly an adventure story, the good fugitives vs. the Big Bad Corporation (and/or Government). A key ingredient is missing.