I personally don't have any huge issues with INS (though I could have done with less of the cutsie Data-Artem stuff) it's no TFF!
NEM was just bad. Gaping plot holes and story elements that made little sense (Worf and Wesley back in uniforms, Shinzon's hatred of a planet he's never set foot on, pointless nature-vs-nurture debates between Picard and Shinzon, the fact that there are uncharted planets along the Neutral Zone [probably the best patrolled region of space there is], Troi seemingly unable to press buttons by herself), needless buggy ride on an world where aliens are hostile for no reason, the E-E growing multiple decks with a massive chasm that goes nowhere and does nothing.
But the biggest thing that ticks me off about that film is B-4 and the fact that Data's death is cheapened by having him there as a back-up at the end of the film. If they are going to kill off Data, then do it and do it right (don't do a Spock and leave a loophole in there in case more films get made).