I wrote an article about Sierra as an innovative company looking to it from the side of innovation, business strategy and markerting: http://www.eoi.es/blogs/redinnovacionEOI/2015/09/23/sierra-innovacion-videojuegos/
Although it is in Spanish. I only wanted to share it, as although there has been a lot of articles written about Sierra, there is not too much written from that viewpoint.
Thanks,
José Luis Villarig