I know the series quite well and I didn't expect the anime to be exactly the same but it has enough differences that I found it rather irritating. Jared voices Sam, and he's great, and the guy who does Dean is okay (there are intro's by both the show actors so he's still somewhat of a presence, plus he voices the last).
Character wise a great deal of the nuance has been lost as can be expected when it's half-length episodes. While there is an arguable tendency for the show to depict Sam as the smarter, better brother and Dean as more the muscle, within the anime series this is greatly emphasized with Sam being pretty much the main focus and fairly consistently being showcased as the better, smarter etc. brother while Dean is relegated to be a bit of a dim bulb hunter mainly only interesting in killing what he's pointed at, busty babes, and looking after Sam.