As much as I like Tom Hardy it would have been a much more fun movie if Patrick Stewart played Shinzon as well as Picard. I agree that the plot could have been much more interesting if Shinzon/Picard actually worked together. It's a problem for me that Shinzon neither looks nor acts like Picard.
Now take a look at Looper for a movie with two different actors's playing the same person, I find it much better - even with Joseph Gordon Levitt's strange face. Imagine if they just shaved JGL's head and said, it's young bruce willis! That would suck, and that's what they did here.
The line that's like "our hearts are the same" bugs me. You've got an artificial heart Picard.
I like it better than Generations but less than the rest of the movies. I find Insurrection far better.