For this gun, many players have their own opinions. I've read a lot of articles about the Roar; some say it's good, others say it's not so great. For me, at the time when I hadn't used it yet, relying solely on others' experiences wasn't enough because you really need to try it yourself to know. Here, we're only talking about the Biohazard mode.
Briefly: The Roar is an armor-piercing gun, dealing more damage to the head, but if you hit anywhere other than the head, the damage drops significantly.
Source of this article: CS Counter-Strike Elite Station (www.cszhan.com). Detailed reference: http://www.cszhan.com/csol-gonglue/csol4220.html