The main thing I found about the Supernatural anime was I really didn't like their interpretation of Dean. Sam I thought was good, but Dean, he was pretty ridiculous. The faux Jensen did a decent job on the voice, but the character lacked the depth Dean has. Also, the script here and there was horrible and everyone wore hats, Bobby, John, the YED, which struck me as odd. It was a little peculiar to hear Jared, who voiced all 22 eps as Sam, bouncing off faux Jensen/Dean. When they brought Jensen in for the final 2 eps of the season, it improved out of sight. I know I'm one eyed, but honestly it did! He is a damn good actor and it just brought the level up. One thing I liked though was the visuals...they were pretty dang cool and over the top.
Anyway, here are a couple of compiles of interview grabs of the boys talking about the Supernatural anime, prior to it's release.