For the most part I think that the arc was handled very well. I was surprised to hear the anime bring up the whole idea about humans and pokemon being separated, especially with N's sisters. N himself was also handled very well although he could be a bit reckless at times (jumping in front of an attack and such.) Colress was the best thing to come out of that arc. I loved his entire character.
The things I didn't like as much were
1, the random filler episodes thrown into the arc. Those episodes could have easily gone anywhere else in BW.
2, Not going more into Ghetsis' and N's relationship. In the games Ghetsis is N's father but that's not mentioned at all in the anime. In fact the two didn't really speak that much anyway.
3, The fact that Ghetsis barely did a thing. All he really did was awaken Reshiram. It was Colress who was doing pretty much all of the work.
4, No mention of the other Seven Sages besides in a brief flashback, and even then they weren't mentioned, just shown.
Overall, Episode N was pretty much the best arc to come out of BW. It did feel really rushed towards the end but at least they actually gave N an arc of his own instead of just not showing him at all.