Yeah Nero didn't have much depth and sadly there wasn't much time to give him some, I agree though that a scene showing his pain may have helped somewhat. To be honest the only new villain in the films that was effective was Chang (excluding the Borg Queen as it was suggested that her and Picard had interacted during BOBW so wasn't truly new to the crew and audience in that respect).
And since nuTrek has no real background leading up to the films it would be difficult to produce a really good villain who doesn't have any history with the crew that would match up to good villains we've seen in previous films. We've seen the results of trying to create villains off the cuff with the likes of Soren and Ruafo who are arguably the poorer of the movie villains.
Personally I would like to see a villain more in the guise of V'Ger as in a palpable threat that's wondrous and totally alien at the same time.