As a woman, i interpret the "too nice" thing 2 ways:
First, he's too eager. If i'm not sure about a guy (which you probably shouldn't be when you first meet him), but he's soooooo sure i'm the one for him, it's a little bit scary. Not necessarily in a stalker way, but more scary in the sense that i don't want to reciprocate and end up breaking his heart when i find out i don't like him as much as he likes me. That's just a big mess.
Second, he's literally too nice. He takes me, or life in general too seriously. He's not willing to make me the butt of a joke. He seems so nice, that i seem like a total bitch in comparison b/c i make jokes about people, i criticize, i self-deprecate, i'm not overly sensitive. Am i a nice person? Of course i am, but i'm no angel, and maybe having an angel around is a little bit too much for me to handle.
