My first impression of your site was: "made for Adsense". Forgive me
for being blunt, but I just wanted to put it out there.

Now I don't know what the original goal of the site was, but the way
it looks now appears to be a collection of articles with a big block
of Adsense above the fold. Reading through some of the articles, they
appear to be very, very broad and feel ... "unpersonal" (hard to put
it into words).

My gut feeling is that Google is recognizing that the site consists of
unrelated articles that do not have much merit of their own. Compared
to say a Wikipedia your articles most likely do not have direct
support through links from other sites.

Additionally, while I can't trace it directly, it appears as if your
articles were either written by a "cheap" copywriter or copied from
other sites, perhaps modified so as not to be full copies. Finding
things like that is a bit hard for us "mortals" since we do not have
access to the full datasets directly, but I am fairly certain that
Google can determine "near duplicates" or "modified duplicates" of
content (it would only make sense). You can see near duplicates with
http://www.alkenmrs.com/vitamins/ vs http://vitamins-for-health.com/vitamins_and_minerals_facts.html
-- I don't know who's content was up first or where the original
content came from (perhaps from your site), but you can tell that
they're more than just similar.

"Unique and compelling content" .... is your content really, really
that compelling?

What could you do to make it more compelling?

John