The problem as I see it is simply this:
In Nemesis, we are asked to believe that someone that looks like a 17 year old kid is going to tangle and hold his own with a respected mature captain like Picard, AND we are asked to believe that this person IS Picard, only younger?
It just doesn't work. Like I said before, it may have worked on Paper, but it didn't transfer to the big screen. The sad thing is that there's simple things they could have done to fix this problem. For one, don't be pretentious in your introduction of the character. What was with the waiting 18hr or whatever it was, and then all the secrecy about who he is, even to the last moment when he slowwwwwwwwwly steps into the light for the big reveal that....gasp!......he looks just like Picard

. What was this supposed to prove? Was it some lame attempt at trying to convince the audience that this person was Picard's clone? Why is he bald? Why is he taking FOREVER to get shit done????
nuStar Trek did it the right way, Nero appears on screen saying "Hi Christopher, I'm Nero" bam!! the authority that scene had was amazing, like the guy was saying "Hi cockroaches, I'm Nero", and he doesn't waste any time, he lets all cannons loose almost immediately.
The whole time Shinzon was acting like a brat and emo beeyatch, I kept thinking back to the lines in TMP when Spock said "V'Ger is a child" and McCoy goes "well, what do you suggest we do, spank it?". That's how I felt the entire movie, Shinzon needed a good spanking. The rape scene just made him look even more like a creepy pervert, like the 17 year old in mom's basement with the terabytes of triple x rated material.
Nero on the other hand, even if the character wasn't fleshed out the same, actually felt like an adult. A whacko crazed nut who would stab you while you're looking at him, but adult none the less, and far more terrifying.