The Metal Crypt posted an article compiling opinions of other musicians on Possessed's 'Seven Churches' album in honour of its 30th anniversary. I found the article linked from Possessed's Facebook page:
http://www.metalcrypt.com/pages/interviews.php?intid=455
It's definitely a long read, but worth it to gain insight into just how influential this album became. I can't personally speak to the evolution of 'Seven Churches' influence, nor can I speak to the impact it had when first released as I have found Possessed relatively recently. The first time I truly took notice of the band was on the Barge To Hell cruise, and I consider myself lucky to have caught them live again at Noctis Festival a few years ago.
Even all of these years after Possessed began, I was blown away by the intensity of their live show. Especially considering that I did not even realize Jeff Becerra is in a wheelchair until the band took the stage. Live, they managed to be one of the most evil sounding bands I've seen without having to use theatrics. 'Seven Churches' has become an album that I thoroughly enjoy, and one that I believe anyone studying the roots of death metal should own.