I think the unclean beast is good, I think part of the issue right now is that some demigods are too good. Right now stuns are very powerful as well and can cripple the beast, but I know that's already slated to be reworked.
The thing with the Beast is, IMO, he's not a front-line fighter and a lot of people try to play him as such. Get his movement speed up and he's fantastic as sticking and running, he just can't stand stand there and take a beating. Add in plagues, ooze, and liberal use of Beastial Wrath and he can tear people up.
One thing he could use is a getaway ability, perhaps a Sprint-like ability that allows him to break roots/stuns and gives him a temporary movement speed buff.
There's an achievement item that gives a chance to boost attack speed by a large amount. Equip that thing and flip on bestial wrath and it's just... sickening... what he can do.