Nadia is... a complicated character. She is a vegetarian, naive, and a pessimist. She doesn't trust others easily and often snaps in anger at those around her. She's a bit annoying at times, but she improves as her character develops.
However, the Island and Africa episodes make her a completely insufferable bitch that you just want to strangle. All of her development seems to have gone out the door. Also, everyone's IQ seems to have lowered as well. Oh, and crappy cartoon physics that were never there before.
Thankfully, most of these episodes are disregarded on the final arc.