Personally I loved Nemesis but I think that what a lot of people had a problem with was the lazy writing as the Story is basically a rehash of The Wrath of Khan and to a lesser extent The Search for Spock.
Both Villains were genetically engineered.
Khan blamed Kirk for the death of his wife for stranding them on Ceti Alpha V and this seeds the drive for his vengeance.
Shinzon blames Picard for his existence stating that Picard had everything and he had nothing, they were the products of environment not of genetics.
Khan's quest for Vengeance ultimately destroys him in that his vendetta against Kirk compels him to fight pursue kirk, kirk in fact goads him questioning the "Superior Intellect"
Likewise it is Shinzons hatred for Picard that leads to his destruction, Picard realises that Shinzon will pursue him and draws him away from Earth. Shinzon even says that it is too bad he will not witness the victory of the Echo over the Voice.
The Final Battle of both films takes place in a Nebula and the interfering nature of the nabula is a big plot device in both films furthermore in both films the captains win the respective battles via an epiphany that comes from the knowledge of their enemy although this is slightly more profound in the case of Picard.
Helped by Spock, Kirk realises that Khan is using 2 dimensional tactics and adjusts his tactics to compensate and defeat Khan.
Picard actually says "We've got him" and then goes on to say Shinzon thinks he knows what he is going to do so then Picard acts totally unpredictably and orders the Enterprise to Ram the Scimitar while distracting Shinzon.
Both films are Centred around a Doomsday Weapon, The Genesis Device and Thalaron weaponry.
Both villains after they are defeated try to use their weapons to exact their Final vengeance
Both Crews are saved by the Inhuman element of the crew in what turns out to be a very Human act as they sacrifice themselves to save others. Spock and Data.
Spock is resurrected in on the Genesis planet and then he is given his katra back from Mccoy. Transversely Data trys to share his mind with B4 and apparently fails however at the end of the film starts to sing Blue Skies.
So these are the main similarities but there are other subtle similarities!