If you want to hire based on "intelligence" (ick), create an assessment rubric that surfaces the kind of intelligence you're looking for. Don't rely on face-to-face meetings to do that; it doesn't work.
Did you hire on any sort of "personality fit" at all? I.e. would you hire a technically brilliant asshole?
Personally, I really try to be objective, ask the same questions every time, etc.. but lately I realized that if you're going to be spending 40+ hours per week with a person, it's not just the matter of them getting their job done...you also need to be able to work together, and that does require some amount of congruency in personality styles