Getting to know you

So....you & another person start the 'getting to know you dance' on-line. 1 of you has a personal ad up somewhere, the other 1 of you responded to it....and you've exchanged a few emails. 1 of you states unequivocally---I want to get to know you, tell me anything about yourself that you are comfortable with telling me. The other 1 of you starts talking about yourself but also tries to draw out personal things from the 1st person....so that the conversation isn't completely ME ME ME & 1 sided. Then suddenly....1 of you decides that this isn't really going to go anywhere....there's some basic incompatibility that has come to light. So....do you just stop 'talking' to the person all together, leaving them to possibly wonder "what happened?", or do you write them 1 last email and let them know that you don't think you're all that compatible after all?