well its a system, so its value is dependent on the other values but it would be quite important. Its more important that a title tag or any on page SEO. As a single determinant factor, it could be described as the most important. But then, look at Geo-location ability, Authority, Age/History and its the weakest of those, because thats where a site is judged against others. In a market with low-seo quality, it would probably be enough to rank on that factor alone.