Nice and sweet is good at times, but my last boyfriend was REALLY nice and sweet. And I couldn't stand it! When I was in a good mood, then it was fine and I was really pleased that my bf was so lovely, but it did make him a bit of a walkover. So when I was in bad mood and I just wanted someone to argue with I'd pick him up on something and he'd just go 'oh sorry honey, I'm really sorry. I love you' which would infuriate me beyond belief, as I really need someone that will react to me and not just roll over and play dead. And nice guys tend to not be much of a challenge, they just agree with everything you say and support all your ideas. Whereas, its nice to have someone to challenge you every so often.
Sorry, rant over. :-S