I tried one for a few days over the weekend and ended up returning it on Monday and went back to a 5S. I've had an iPhone since the day they were available and thought the N3 would be the phone that took me away from iOS but I was wrong.
The N3 is big, but felt comfortable in hand and wasn't too bad in the pocket either. Much better than the N2 when trying to use it one handed. It took a little adjusting when coming back to the 5S even only after a few days. The iPhone just felt tiny.
One of the big deal breakers for me was build quality. While it has come along nicely when compared to the S3 &S4, it still felt cheap. My N3 had gaps around the screen and the home button was loose and crooked. Coming from the iPhone and every one that I have owned has been flawless, those issues kinda stood out.
I also didn't find the battery life to be that impressive. While it is better than most Android phones I have tried, it still wasn't anything special. For my uses, I'd put it on par with my 5S.
If you could look past the possibility of build quality issues, the size doesn't bother you, and you are ok with Touchwiz, it's a great Android phone. For me however, the iPhone still hits the sweet spot between size, build quality, and functionality. I'm glad to be back even if it was only for a few days.