Shinzon

Shinzon is the primary villain of the film Star Trek: Nemesis. He was played by Tom Hardy, and was a clone of the lead character of Nemesis and Star Trek: The Next Generation, Jean-Luc Picard.

Why He's Loathsome

 * 1) Despite being cloned from Jean-Luc Picard, he has almost nothing in common with Picard other than a vaguely similar physical appearance. He's just a generic villain who wants to use a superweapon to cause mass-murder.
 * 2) He was intended to be the TNG crew's counterpart of the classic Star Trek villain Khan Noonien Singh. But Khan worked as a villain because of his history with Captain Kirk and the original Enterprise crew, while Shinzon has no connection with Picard other than happening to share his DNA.
 * 3) Generally he doesn't feel threatening at all, coming across as more angry and petulant than anything else.
 * 4) His motives make absolutely no sense. He was created by the Romulans, then dumped in a mine on the planet Remus and mistreated for decades by his Romulan masters. So, he takes over the Romulan Empire and then decides to exterminate the human race for no reason that's ever explained.
 * 5) * In his original introductory scene, it was revealed that his actual long-term goal was to get the Remans treated equally to the Romulans, with his destroying Earth just being intended to solidify his hold on the Empire long enough for him to actually accomplish that. The scene was deleted in order to preserve the surprise of Shinzon being human, however, meaning that his motives in the finished film seem to involve just destroying Earth for the heck of it.
 * 6) He looks ridiculous, with his outfit making him look like some kind of wannabe goth teenager, and his bald head making him look more like Dr. Evil than Picard. Note that he was written as having hair in the script, but the producer and director didn't think audiences would buy Shinzon as a younger Picard unless he was also bald.
 * 7) Despite urgently needing a transfusion of all of Picard's blood in order to survive, he screws around having dinner with Picard and then arguing with some Romulan generals. The time that he wastes doing this allows the Enterprise crew to detect the planet-killing weapon installed on-board his flagship, and also work out that the simple-minded prototype of Data that they found on a planet near Romulan space has been programmed to do Shinzon's bidding.
 * 8) We're told that the military backed his coup because he's a great general and war hero. But in the final battle, he does nothing to demonstrate this, only coming close to defeating the Enterprise because he's in a ridiculously overpowered ship.
 * 9) At the end of the battle, a failed kamikaze attack by the Enterprise leaves Shinzon's flagship damaged but still mostly operational, and the Enterprise itself hopelessly crippled. Instead of taking advantage of the perfect opportunity to recapture Picard, then heading off to destroy Earth, Shinzon decides to use his planet-killing weapon on the Enterprise, even though this'll kill Picard, and therefore himself in the longer run.
 * 10) He has a very anti-climatic death, when he stupidly runs into a sharp metal pole that Picard's holding and fatally impales himself.

Redeeming Qualities

 * 1) Tom Hardy gives a good performance in the role, with the few moments that Shinzon does feel threatening being more down to Hardy's acting than anything else.
 * 2) His backstory's at least a little more interesting than those of some of the other Star Trek film villains.