There have been two major revisions to the way in which Google indexed your site in its search algorith. These were called Panda and Penguin. The most significant change is to encourage web site owners to improve the content of their web sites. The more useful and education material that is placed in a web site will in future improve the natural ranking.
The days when all you needed to do was to increase the number of backlinks to your site are gone and the suggestion by some is that SEO may well be over, that SEO companies will struggle to make improvements to a web site ranking without writing good copy for inclusion in the site.
This suggests that in addition to simply having a web site that is a portfolio of goods and services, additional value wil be placed on those sites that add useful and informative comment. This in some ways is very sensible as it encourages wite administrators to include copy that will be of wider benefit to students and people who generally surf the net for information.