Unless Sudden Attack has been buffed on this version since I've stopped playing, it is nearly useless.

What you need to do is make your Moral Rising level 6, and 7 if possible. Level 6 gives you around a 20% boost in critical hit damage, at 7 that's around 40%. It doesn't say it in the description, but it's there.

Mortal Rising does NOT make skills crit if you use them when hiding, it only works for normal hits.

If you REALLY want to use Sudden Attack, and you're going to be a Predator, I think Hide Spirit is what you need. It lets you use Sudden Attack when not hiding, if I remember correctly.