Nah, I don't think being a bad kisser is necessarily a deal-breaker -- IF he is open to some training from you on how you like it.
That's the thing here: everybody likes it different. His last girlfriend might've dug the way he kisses. I've been with women who liked short, soft kisses and others who wanted to eat my face off. I've had women put their tongue in my mouth on the first kiss, and some who never wanted to use their tongue at all. Everyone is different. Me, I'm not picky -- I'll do it however you want it if it means we get to keep doing it, because this is fun and something strange and wonderful is happening in my pants.
I realize that there are certain things that are universally considered lousy kissing form (licking, for example), but whether kissing is "bad" or "good" is at least a little bit subjective. That's why you just need to show him how you like to be kissed. He might have his own preferences, too. It's all about negotiation and compromise and adapting.
I also don't think that "bad" kissing necessarily means he's a bad lover. He might not do it the way you like, but again, you can tell him what you want and see how he responds. If he's unable or unwilling to accommodate you, then you have something to worry about. But I think it's too soon to give up on the guy just yet.