Nemesis. It was just horrible. Data being blown to smithereens then being replaced by the lesser B4. The whole thing about Picard having a clone.... The only highlight was the Wedding scene.
The B4 replacement aspect was awful. Better to have B4 serve a purpose... like destroying the Theleron weapon. Consider a situation in which the weapon was active. No human could get close due to the damaging effects. Data is our only hope. Suddenly, he realizes that he needs a second set of hands. Enter B4. Let them both make the ultimate sacrifice. After all, Spiner's not coming back.