regarding ventress, she has a more threatening role in the clone wars graphic novels. its said because her master was a jedi. he was killed by some inhabitants while on an assignment. that's why she's so evil.
she's supposed to have a role where she digs in hard on flesh and wipes out multiple clones at once. in fact, her and obi wan have a rivalry against each other. so far, i've seen none of that in the series.