[Lewisham]

There are plenty of metrics, like engagement, enjoyment etc. etc., but there is some very tangible metric bar by which games are measured, it's called peer approval.

By what metric are other art forms judged? How are the Oscars awarded to movies? Who chooses the winner of the Booker prize? Or the VMAs? Peer approval.

Zynga doesn't have peer approval from many game designers. This article highlights some dissenting opinion, but there's plenty more out there. Just Google it. Their infamous speech speech at GDC Awards show doesn't help their cause either. [1]

Note I am careful not to say "games reviewers" because reviewers are writing for their audience, and that core game audience usually does not intersect with Zynga.

[1]: http://news.cnet.com/8301-13772_3-20002221-52.html