Sometimes, it takes a second, third, or even fourth date to determine whether or not you want to see more of him.
And for me, I try to stay away from offering my opinion (i.e. "I think you're a nice guy, but ... etc.) .... in reality, the man isn't really interested in our opinion; he's interested in seeing you again and wants your concurrence. If he cannot get that, then a simple "thank you, but no, thank you" can help soften the blow; and if he's a reasonable, rational individual, he will understand and accept it. It's not our intention to hurt him, yet it is our intention to be honest; so with that simple "no, thank you," though it may sting him for a moment, he can't balk at your honesty.
Sometimes, sadly, life is difficult ... so is love ... even more so is rejection ... but everyone is not for everyone else. The sooner we understand and accept that, the better off we all will be.
Just some of my .... hope you meet your Prince Charming real soon, Julie!