I didn't like him much at all the first time I watched the film. But Nero didn't seem that bad on second viewing, but I can't say if that's because I appreciated him and Bana's portrayal more or because my expectations had already been sufficiently lowered.
I think Nero's best moment was the scene where he killed Robau. After that he fell off. He was a weak villain. Kruge, Chang, Borg Queen, Soran, Shinzon and Ru'afo all had more depth. In particular, Shinzon and Ru'afo seethed in a way Nero never really did. I'm still off put by the "Hello I'm Nero" line or him calling Pike by his first name.
One of my friends thought it was a way that Nero showed disrespect, and a poster on one of these forums thought it was Nero being true to his humble roots, but I still didn't care for the line.
There was too much of Nero's backstory not explained. If you didn't read Countdown, you wondered where did a miner get a ship like that? And where did that ship come from? Even the Scimitar looked something like a Romulan warbird, a mutated one perhaps.
There wasn't enough time spent on Nero, showing his pain, his hurt, and how that twisted him into a man bent on revenge. He was a poor man's Khan, without the charm or the backstory to build on. I think Nero's character would've been better served with a couple scenes set in the 24th century Countdown-style to show his relationship with Spock before things went sour, so that the audience can get a better understanding of why he hates and blames Spock so much. I think part of Spock's retelling of how he failed to save Romulus should've been said by Nero.