Yes, there are almost three classes of force users in that era. The republic are traditional good Jedi. The Empire version is almost a "grey" jedi, and the One Sith are the extention of the traditional evil Sith.
Darth Talon is one of the more brutal and vicious Sith. Most Sith seem to have a tendency to kill as a means to gain power and influence. She just likes to kill without any other motivation or justification needed. She is one of the most visually striking characters to come out of the Star Wars universe in awhile. Even though is is a heartlees, evil, ***** is certianly reinforces that Twi'leks look awsome.
While many claim the legacy era loyalist empire jedi are "grey" I do not see them as so. They are Jedi. They believe in the Living force and serve the Emperor as he is the physical embodiment of the living force. That is, in their belief system at least. They simply do not serve the republic/rebel alliance.
A "grey" Jedi for me would have to be one who follows the belief of the Unifying Force. As they believe there is no light or dark.. Just the force.
And yes, Darth Talon was a sexy she-beast who was a sadistic killer, but also loyal Krayt and also shown as having a heart in that she seems to have a bit of a soft spot for Cade. If I remember that portion correctly.